diff --git a/Config/Languages/en-US/Chrome.json b/Config/Languages/en-US/Chrome.json
index 68ddd27..4ab2c14 100644
--- a/Config/Languages/en-US/Chrome.json
+++ b/Config/Languages/en-US/Chrome.json
@@ -6,6 +6,15 @@
   "MessageBoxNo": "No",
   "TitleBarSupportCreator": "Support the creator",
   "TitleBarOptions": "Options",
+  "SettingsTitle": "Settings",
+  "SettingsSave": "Save",
+  "SettingsTheme": "Theme",
+  "SettingsThemeAuto": "Auto",
+  "SettingsThemeLight": "Light",
+  "SettingsThemeDark": "Dark",
+  "SettingsLanguage": "Language",
+  "SettingsLanguageAuto": "System default",
+  "SettingsSaveError": "Unable to save settings. Please try again.",
   "TitleBarClose": "Close",
 
   "MenuImportConfig": "Import config",
diff --git a/Config/Languages/nl-NL/Chrome.json b/Config/Languages/nl-NL/Chrome.json
index e0041d0..a29d1f2 100644
--- a/Config/Languages/nl-NL/Chrome.json
+++ b/Config/Languages/nl-NL/Chrome.json
@@ -6,6 +6,15 @@
   "MessageBoxNo": "Nee",
   "TitleBarSupportCreator": "Steun de maker",
   "TitleBarOptions": "Opties",
+  "SettingsTitle": "Instellingen",
+  "SettingsSave": "Opslaan",
+  "SettingsTheme": "Thema",
+  "SettingsThemeAuto": "Automatisch",
+  "SettingsThemeLight": "Licht",
+  "SettingsThemeDark": "Donker",
+  "SettingsLanguage": "Taal",
+  "SettingsLanguageAuto": "Systeemstandaard",
+  "SettingsSaveError": "Kan de instellingen niet opslaan. Probeer het opnieuw.",
   "TitleBarClose": "Sluiten",
   "MenuImportConfig": "Configuratie importeren",
   "MenuImportConfigTooltip": "Configuratie importeren",
diff --git a/Config/Languages/nl-NL/Features.json b/Config/Languages/nl-NL/Features.json
index a4b88a8..36664f8 100644
--- a/Config/Languages/nl-NL/Features.json
+++ b/Config/Languages/nl-NL/Features.json
@@ -478,7 +478,7 @@
     },
     "HideHome": {
       "Label": "'Start' in het navigatievenster verbergen",
-      "ToolTip": "Verbergt de sectie 'Start' in het navigatievenster van Verkenner. Waarschuwing: dit kan ervoor zorgen dat snelkoppelingen in Snelle toegang niet worden bijgewerkt totdat je je pc of Verkenner opnieuw opstart."
+      "ToolTip": "Verbergt de sectie 'Start' in het navigatievenster van Verkenner. Waarschuwing: dit kan ervoor zorgen dat snelkoppelingen in Snelle toegang niet worden bijgewerkt totdat je je pc of Verkenner opnieuw opstart.",
       "ApplyText": "De sectie 'Start' in het navigatievenster van Verkenner verbergen",
       "UndoLabel": "'Start' in het navigatievenster tonen",
       "ApplyUndoText": "De sectie 'Start' in het navigatievenster van Verkenner tonen"
diff --git a/Config/Languages/pt-BR/Apps.json b/Config/Languages/pt-BR/Apps.json
new file mode 100644
index 0000000..0967ef4
--- /dev/null
+++ b/Config/Languages/pt-BR/Apps.json
@@ -0,0 +1 @@
+{}
diff --git a/Config/Languages/pt-BR/Chrome.json b/Config/Languages/pt-BR/Chrome.json
index 3e359bc..601553f 100644
--- a/Config/Languages/pt-BR/Chrome.json
+++ b/Config/Languages/pt-BR/Chrome.json
@@ -7,6 +7,15 @@
   "TitleBarSupportCreator": "Apoiar o criador",
   "TitleBarOptions": "Opções",
   "TitleBarClose": "Fechar",
+  "SettingsTitle": "Configurações",
+  "SettingsSave": "Salvar",
+  "SettingsTheme": "Tema",
+  "SettingsThemeAuto": "Auto",
+  "SettingsThemeLight": "Claro",
+  "SettingsThemeDark": "Escuro",
+  "SettingsLanguage": "Idioma",
+  "SettingsLanguageAuto": "Padrão do sistema",
+  "SettingsSaveError": "Não foi possível salvar as configurações. Tente novamente.",
 
   "MenuImportConfig": "Importar configuração",
   "MenuImportConfigTooltip": "Importar configuração",
diff --git a/Schemas/MainWindow.xaml b/Schemas/MainWindow.xaml
index 5956ec7..7a7aa94 100644
--- a/Schemas/MainWindow.xaml
+++ b/Schemas/MainWindow.xaml
@@ -363,6 +363,7 @@
                         </TextBlock>
                         <StackPanel Grid.Column="1" Orientation="Horizontal">
                             <Button x:Name="KofiBtn" shell:WindowChrome.IsHitTestVisibleInChrome="True" Content="&#xEB52;" FontSize="15" Style="{StaticResource TitlebarButton}" ToolTip="%LANG:TitleBarSupportCreator%" AutomationProperties.Name="%LANG:TitleBarSupportCreator%"/>
+                            <Button x:Name="SettingsBtn" shell:WindowChrome.IsHitTestVisibleInChrome="True" Content="&#xE713;" FontSize="15" Style="{StaticResource TitlebarButton}" ToolTip="%LANG:SettingsTitle%" AutomationProperties.Name="%LANG:SettingsTitle%"/>
                             <Button x:Name="MenuBtn" shell:WindowChrome.IsHitTestVisibleInChrome="True" Content="&#xE700;" FontSize="15" Style="{StaticResource TitlebarButton}" ToolTip="%LANG:TitleBarOptions%" AutomationProperties.Name="%LANG:TitleBarOptions%">
                                 <Button.ContextMenu>
                                     <ContextMenu x:Name="MainMenu">
@@ -685,23 +686,7 @@
                                         </ScrollViewer>
                                         <Border x:Name="LoadingAppsIndicator" CornerRadius="0,0,4,4" Background="{DynamicResource CardBgColor}" Opacity="0.8" Visibility="Collapsed">
                                             <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center">
-                                                <TextBlock Text="&#xF16A;" FontFamily="{DynamicResource AppIconFontFamily}" FontSize="28" Foreground="{DynamicResource AppFgColor}" HorizontalAlignment="Center" Margin="0,0,0,8" RenderTransformOrigin="0.5,0.5">
-                                                    <TextBlock.RenderTransform>
-                                                        <RotateTransform Angle="0"/>
-                                                    </TextBlock.RenderTransform>
-                                                    <TextBlock.Triggers>
-                                                        <EventTrigger RoutedEvent="Loaded">
-                                                            <BeginStoryboard>
-                                                                <Storyboard>
-                                                                    <DoubleAnimation Storyboard.TargetProperty="(UIElement.RenderTransform).(RotateTransform.Angle)"
-                                                                                     From="0" To="360"
-                                                                                     Duration="0:0:1.5"
-                                                                                     RepeatBehavior="Forever"/>
-                                                                </Storyboard>
-                                                            </BeginStoryboard>
-                                                        </EventTrigger>
-                                                    </TextBlock.Triggers>
-                                                </TextBlock>
+                                                <TextBlock Style="{DynamicResource LoadingSpinnerStyle}" Margin="0,0,0,8"/>
                                                 <TextBlock Text="%LANG:AppLoadingIndicator%" FontSize="16" FontWeight="SemiBold" Foreground="{DynamicResource AppFgColor}" HorizontalAlignment="Center"/>
                                             </StackPanel>
                                         </Border>
diff --git a/Schemas/SettingsWindow.xaml b/Schemas/SettingsWindow.xaml
new file mode 100644
index 0000000..e762c60
--- /dev/null
+++ b/Schemas/SettingsWindow.xaml
@@ -0,0 +1,71 @@
+<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+        Title="%LANG:SettingsTitle%" Width="500" SizeToContent="Height"
+        ResizeMode="NoResize" WindowStartupLocation="CenterOwner" WindowStyle="None"
+        AllowsTransparency="True" Background="Transparent" ShowInTaskbar="False">
+    <Border Style="{DynamicResource ModalCardBorderStyle}">
+        <Grid>
+            <Grid.RowDefinitions>
+                <RowDefinition Height="Auto"/>
+                <RowDefinition Height="Auto"/>
+                <RowDefinition Height="Auto"/>
+            </Grid.RowDefinitions>
+            <Grid x:Name="TitleBar" Style="{DynamicResource ModalTitleBarStyle}">
+                <TextBlock Text="%LANG:SettingsTitle%" Style="{DynamicResource ModalTitleTextStyle}" HorizontalAlignment="Left"/>
+            </Grid>
+            <Button x:Name="CloseBtn" Grid.Row="0"
+                    HorizontalAlignment="Right" VerticalAlignment="Top"
+                    Width="36" Height="32"
+                    BorderThickness="0" IsCancel="True"
+                    Cursor="Hand"
+                    ToolTip="%LANG:TitleBarClose%"
+                    AutomationProperties.Name="%LANG:TitleBarClose%">
+                <Button.Template>
+                    <ControlTemplate TargetType="Button">
+                        <Border Background="{TemplateBinding Background}" BorderThickness="0" CornerRadius="0,8,0,0">
+                            <ContentPresenter HorizontalAlignment="Center" VerticalAlignment="Center"/>
+                        </Border>
+                    </ControlTemplate>
+                </Button.Template>
+                <Button.Style>
+                    <Style TargetType="Button">
+                        <Setter Property="Background" Value="Transparent"/>
+                        <Setter Property="Foreground" Value="{DynamicResource AppFgColor}"/>
+                        <Style.Triggers>
+                            <Trigger Property="IsMouseOver" Value="True">
+                                <Setter Property="Background" Value="{DynamicResource TitleBarCloseHoverColor}"/>
+                            </Trigger>
+                        </Style.Triggers>
+                    </Style>
+                </Button.Style>
+                <TextBlock Text="&#xE8BB;" FontFamily="{DynamicResource AppIconFontFamily}" FontSize="10"/>
+            </Button>
+            <StackPanel Grid.Row="1" Margin="20,4,20,10">
+                <TextBlock Text="%LANG:SettingsTheme%" Style="{DynamicResource ModalInfoLabelTextStyle}" HorizontalAlignment="Left" Margin="0,0,0,10"/>
+                <UniformGrid Columns="3" Margin="0,0,0,20">
+                    <Button x:Name="ThemeAutoButton" Tag="Auto" Style="{DynamicResource SecondaryButtonStyle}" Height="32" Padding="12,0" Margin="0,0,6,0" AutomationProperties.Name="%LANG:SettingsThemeAuto%">
+                        <StackPanel Orientation="Horizontal"><TextBlock Text="&#xE770;" FontFamily="{DynamicResource AppIconFontFamily}" Margin="0,0,8,0" VerticalAlignment="Center"/><TextBlock Text="%LANG:SettingsThemeAuto%"/></StackPanel>
+                    </Button>
+                    <Button x:Name="ThemeLightButton" Tag="Light" Style="{DynamicResource SecondaryButtonStyle}" Height="32" Padding="12,0" Margin="3,0,3,0" AutomationProperties.Name="%LANG:SettingsThemeLight%">
+                        <StackPanel Orientation="Horizontal"><TextBlock Text="&#xE706;" FontFamily="{DynamicResource AppIconFontFamily}" Margin="0,0,8,0" VerticalAlignment="Center"/><TextBlock Text="%LANG:SettingsThemeLight%"/></StackPanel>
+                    </Button>
+                    <Button x:Name="ThemeDarkButton" Tag="Dark" Style="{DynamicResource SecondaryButtonStyle}" Height="32" Padding="12,0" Margin="6,0,0,0" AutomationProperties.Name="%LANG:SettingsThemeDark%">
+                        <StackPanel Orientation="Horizontal"><TextBlock Text="&#xE708;" FontFamily="{DynamicResource AppIconFontFamily}" Margin="0,0,8,0" VerticalAlignment="Center"/><TextBlock Text="%LANG:SettingsThemeDark%"/></StackPanel>
+                    </Button>
+                </UniformGrid>
+                <TextBlock Text="%LANG:SettingsLanguage%" Style="{DynamicResource ModalInfoLabelTextStyle}" HorizontalAlignment="Left" Margin="0,0,0,10"/>
+                <ComboBox x:Name="SettingsLanguageCombo" AutomationProperties.Name="%LANG:SettingsLanguage%"/>
+                <TextBlock x:Name="SettingsErrorText" Style="{DynamicResource ModalSubtextStyle}" Visibility="Collapsed" Margin="0,12,0,0"/>
+            </StackPanel>
+            <Border Grid.Row="2" Style="{DynamicResource ModalFooterBorderStyle}">
+                <Grid>
+                    <Grid.ColumnDefinitions>
+                        <ColumnDefinition Width="*"/>
+                        <ColumnDefinition Width="*"/>
+                    </Grid.ColumnDefinitions>
+                    <Button x:Name="SaveButton" Grid.Column="1" Content="%LANG:SettingsSave%" IsDefault="True" Padding="12,0" Style="{DynamicResource ModalPrimaryStretchedButtonStyle}"/>
+                </Grid>
+            </Border>
+        </Grid>
+    </Border>
+</Window>
diff --git a/Schemas/SharedStyles.xaml b/Schemas/SharedStyles.xaml
index 9aadf37..fc5375d 100644
--- a/Schemas/SharedStyles.xaml
+++ b/Schemas/SharedStyles.xaml
@@ -1,6 +1,30 @@
 <ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
 
+    <!-- Loading spinner for app inventory. -->
+    <Style x:Key="LoadingSpinnerStyle" TargetType="TextBlock">
+        <Setter Property="Text" Value="&#xF16A;"/>
+        <Setter Property="FontFamily" Value="{DynamicResource AppIconFontFamily}"/>
+        <Setter Property="FontSize" Value="28"/>
+        <Setter Property="Foreground" Value="{DynamicResource AppFgColor}"/>
+        <Setter Property="HorizontalAlignment" Value="Center"/>
+        <Setter Property="RenderTransformOrigin" Value="0.5,0.5"/>
+        <Setter Property="RenderTransform"><Setter.Value><RotateTransform Angle="0"/></Setter.Value></Setter>
+        <Style.Triggers>
+            <Trigger Property="IsVisible" Value="True">
+                <Trigger.EnterActions>
+                    <BeginStoryboard x:Name="LoadingSpinStoryboard">
+                        <Storyboard>
+                            <DoubleAnimation Storyboard.TargetProperty="(UIElement.RenderTransform).(RotateTransform.Angle)"
+                                             From="0" To="360" Duration="0:0:1.5" RepeatBehavior="Forever"/>
+                        </Storyboard>
+                    </BeginStoryboard>
+                </Trigger.EnterActions>
+                <Trigger.ExitActions><RemoveStoryboard BeginStoryboardName="LoadingSpinStoryboard"/></Trigger.ExitActions>
+            </Trigger>
+        </Style.Triggers>
+    </Style>
+
     <!-- Primary Button Style -->
     <Style x:Key="PrimaryButtonStyle" TargetType="Button">
         <Setter Property="Background" Value="{DynamicResource ButtonBgColor}"/>
diff --git a/Scripts/FileIO/Import-LanguageFile.ps1 b/Scripts/FileIO/Import-LanguageFile.ps1
index 5941506..9e8bd89 100644
--- a/Scripts/FileIO/Import-LanguageFile.ps1
+++ b/Scripts/FileIO/Import-LanguageFile.ps1
@@ -1,3 +1,36 @@
+<#
+    .SYNOPSIS
+        Returns the required language catalog names.
+
+    .OUTPUTS
+        System.String. The required catalog names.
+#>
+function Get-LanguageCatalogNames {
+    return @('Chrome', 'Features', 'Categories', 'Apps')
+}
+
+<#
+    .SYNOPSIS
+        Lists language folders containing every required JSON catalog.
+
+    .PARAMETER LanguagesPath
+        The directory containing language folders. Defaults to $script:LanguagesPath.
+
+    .OUTPUTS
+        System.IO.DirectoryInfo. The available language folders.
+#>
+function Get-AvailableLanguageFolders {
+    param([string]$LanguagesPath = $script:LanguagesPath)
+
+    $catalogNames = Get-LanguageCatalogNames
+    foreach ($folder in (Get-ChildItem -LiteralPath $LanguagesPath -Directory | Sort-Object Name)) {
+        $missingCatalogs = @($catalogNames | Where-Object {
+            -not (Test-Path -LiteralPath (Join-Path $folder.FullName "$_.json") -PathType Leaf)
+        })
+        if ($missingCatalogs.Count -eq 0) { $folder }
+    }
+}
+
 <#
     .SYNOPSIS
         Resolves a language code to an available Config/Languages folder, or falls back to en-US.
@@ -35,22 +68,19 @@ function Import-LanguageContent {
     )
 
     $folderPath = Join-Path $LanguagesPath $LanguageFolder
-    $chrome = Import-JsonFile -filePath (Join-Path $folderPath 'Chrome.json')
-    $features = Import-JsonFile -filePath (Join-Path $folderPath 'Features.json')
-    $categories = Import-JsonFile -filePath (Join-Path $folderPath 'Categories.json')
-    $apps = Import-JsonFile -filePath (Join-Path $folderPath 'Apps.json')
-
-    if (-not $chrome -or -not $features -or -not $categories -or -not $apps) {
-        return $null
+    $catalogs = @{}
+    foreach ($name in (Get-LanguageCatalogNames)) {
+        $catalogs[$name] = Import-JsonFile -filePath (Join-Path $folderPath "$name.json")
     }
+    if (@($catalogs.Values | Where-Object { -not $_ }).Count) { return $null }
 
     return [PSCustomObject]@{
         LanguageCode = $LanguageFolder
-        Chrome       = $chrome
-        Features     = $features.Features
-        UiGroups     = $features.UiGroups
-        Categories   = $categories
-        Apps         = $apps
+        Chrome       = $catalogs.Chrome
+        Features     = $catalogs.Features.Features
+        UiGroups     = $catalogs.Features.UiGroups
+        Categories   = $catalogs.Categories
+        Apps         = $catalogs.Apps
     }
 }
 
@@ -398,25 +428,33 @@ function Test-LanguageKeyCoverage {
 
 <#
     .SYNOPSIS
-        Substitutes %LANG:Key% markers in XAML text with translated, XML-escaped values.
+        Replaces %LANG:Key% markers with translated text or dynamic language resources.
 
     .DESCRIPTION
-        Only resolves flat Chrome.json keys, since XAML markers never reference a Feature/Category/
-        UiGroup field directly (those get their text from Get-Translation calls in the GUI scripts
-        that build dynamic controls). Runs a single pass over every marker rather than sequential
-        .Replace() calls, so an already-substituted value can't be re-matched by a later key.
+        Resolves Chrome catalog markers using the active language and its English fallback.
+        Supports embedded text or dynamic resources for windows that allow language changes.
+        Throws when a marker's key is missing from both languages.
 
-        After substitution, scans for any %LANG:...% text that survived unresolved and throws,
-        since Get-Translation's key-as-fallback behavior means a missing key would otherwise render
-        as plain, un-marked text (e.g. "TitleBarClose" instead of a visible error) rather than being
-        caught here. Checks both the active language and its Fallback before flagging a key missing,
-        so a partially-translated language degrades to en-US text instead of failing to load.
+    .PARAMETER Xaml
+        The XAML text containing %LANG:Key% markers to replace.
+
+    .PARAMETER Lang
+        The loaded language object and its optional Fallback. Defaults to $script:Lang.
+
+    .PARAMETER DynamicResources
+        Uses DynamicResource references to Language_<key> resources for live language updates.
+        The window must provide those resources. When omitted, embeds XML-escaped translated text.
+
+    .OUTPUTS
+        System.String. The XAML text with localization markers replaced.
 #>
 function ConvertTo-LocalizedXaml {
     param(
         [Parameter(Mandatory)]
         [string]$Xaml,
-        [object]$Lang = $script:Lang
+        [object]$Lang = $script:Lang,
+        # For live windows, keep a resource reference instead of embedding the translated text.
+        [switch]$DynamicResources
     )
 
     $missingKeys = New-Object System.Collections.Generic.List[string]
@@ -426,6 +464,7 @@ function ConvertTo-LocalizedXaml {
         $key = $match.Groups[1].Value
         $resolvesSomewhere = @(Get-LanguageFallbackChain -Lang $Lang) | Where-Object { $_.Chrome -and $_.Chrome.PSObject.Properties[$key] }
         if (-not $resolvesSomewhere) { $missingKeys.Add($key) }
+        if ($DynamicResources) { return "{DynamicResource Language_$key}" }
         $value = if ($resolvesSomewhere) { Get-Translation -Key $key -Lang $Lang } else { $key }
         return [System.Security.SecurityElement]::Escape($value)
     }
diff --git a/Scripts/GUI/Get-SystemUsesDarkMode.ps1 b/Scripts/GUI/Get-SystemUsesDarkMode.ps1
index 0935654..415a323 100644
--- a/Scripts/GUI/Get-SystemUsesDarkMode.ps1
+++ b/Scripts/GUI/Get-SystemUsesDarkMode.ps1
@@ -7,7 +7,7 @@
 #>
 function Get-SystemUsesDarkMode {
     try {
-        $personalizeKey = Get-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize'
+        $personalizeKey = Get-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize' -ErrorAction Stop
 
         if ($null -eq $personalizeKey) {
             Write-Host "WARNING: Unable to retrieve personalization settings." -ForegroundColor Yellow
diff --git a/Scripts/GUI/MainWindow-AppSelection.ps1 b/Scripts/GUI/MainWindow-AppSelection.ps1
index 08909f9..e5d423d 100644
--- a/Scripts/GUI/MainWindow-AppSelection.ps1
+++ b/Scripts/GUI/MainWindow-AppSelection.ps1
@@ -444,11 +444,12 @@ function Add-AppsToMainWindow {
         $dot = New-Object System.Windows.Shapes.Ellipse
         $dot.Style = $Window.Resources['AppRecommendationDotStyle']
         $dot.Fill = switch ($app.Recommendation) { 'safe' { $brushSafe } 'unsafe' { $brushUnsafe } default { $brushDefault } }
-        $dot.ToolTip = switch ($app.Recommendation) {
-            'safe'   { Get-Translation -Key 'AppLegendRecommendedTooltip' }
-            'unsafe' { Get-Translation -Key 'AppLegendNotRecommendedTooltip' }
-            default  { Get-Translation -Key 'AppLegendOptionalTooltip' }
+        $recommendationKey = switch ($app.Recommendation) {
+            'safe'   { 'AppLegendRecommendedTooltip' }
+            'unsafe' { 'AppLegendNotRecommendedTooltip' }
+            default  { 'AppLegendOptionalTooltip' }
         }
+        $dot.SetResourceReference([System.Windows.FrameworkElement]::ToolTipProperty, "Language_$recommendationKey")
         [System.Windows.Controls.Grid]::SetColumn($dot, 0)
 
         $tbName = New-Object System.Windows.Controls.TextBlock
@@ -479,6 +480,8 @@ function Add-AppsToMainWindow {
         Add-Member -InputObject $checkbox -MemberType NoteProperty -Name 'SelectedByDefault' -Value $app.SelectedByDefault
         Add-Member -InputObject $checkbox -MemberType NoteProperty -Name 'AppIds' -Value @($app.AppId)
         Add-Member -InputObject $checkbox -MemberType NoteProperty -Name 'AppIdDisplay' -Value $app.AppIdDisplay
+        Add-Member -InputObject $checkbox -MemberType NoteProperty -Name 'AppNameText' -Value $tbName
+        Add-Member -InputObject $checkbox -MemberType NoteProperty -Name 'AppDescriptionText' -Value $tbDesc
 
         $checkbox.Add_Checked({
             $w = $script:MainWindow
@@ -574,6 +577,8 @@ function Initialize-MainWindowApps {
     # Prevent concurrent loads
     if ($script:IsLoadingApps) { return }
     $script:IsLoadingApps = $true
+    $settingsButton = $Window.FindName('SettingsBtn')
+    if ($settingsButton) { $settingsButton.IsEnabled = $false }
 
     if ($ImportConfigBtn) {
         $ImportConfigBtn.IsEnabled = $false
@@ -622,6 +627,8 @@ function Initialize-MainWindowApps {
             }
             finally {
                 $script:IsLoadingApps = $false
+                $settingsButton = $Window.FindName('SettingsBtn')
+                if ($settingsButton) { $settingsButton.IsEnabled = $true }
             }
         }) | Out-Null
 }
diff --git a/Scripts/GUI/MainWindow-Localization.ps1 b/Scripts/GUI/MainWindow-Localization.ps1
new file mode 100644
index 0000000..dfd6508
--- /dev/null
+++ b/Scripts/GUI/MainWindow-Localization.ps1
@@ -0,0 +1,147 @@
+<#
+    .SYNOPSIS
+        Populates dynamic language resources for a window and its detached menus.
+
+    .DESCRIPTION
+        Keeps text bound to language resources in sync with the active language, including
+        menus and popups that use separate resources.
+
+    .PARAMETER Window
+        The window whose language resources are updated, along with its menus and popups.
+#>
+function Update-WindowLanguageResources {
+    param([System.Windows.Window]$Window)
+
+    $keys = @(foreach ($language in (Get-LanguageFallbackChain -Lang $script:Lang)) {
+        $language.Chrome.PSObject.Properties.Name
+    }) | Sort-Object -Unique
+    # Popups and context menus can have a separate resource lookup tree.
+    $targets = @($Window, $Window.FindName('MainMenu'), $Window.FindName('PresetsPopup'), $Window.FindName('TweaksPresetsPopup')) | Where-Object { $null -ne $_ }
+    foreach ($key in $keys) {
+        $text = Get-Translation -Key $key -Section 'Chrome'
+        foreach ($target in $targets) { $target.Resources["Language_$key"] = $text }
+    }
+}
+
+<#
+    .SYNOPSIS
+        Refreshes localized text on existing main window tweak controls.
+
+    .DESCRIPTION
+        Updates tweak text and accessibility labels for the active language while preserving
+        existing controls and selections.
+
+    .PARAMETER Window
+        The main window containing the registered dynamic tweak controls.
+#>
+function Update-MainWindowTweakLanguage {
+    param([System.Windows.Window]$Window)
+
+    foreach ($category in $script:CategoryLanguageControls) {
+        $label = Get-Translation -Key $category.CategoryId -Field 'Label' -Section 'Categories'
+        $category.Header.Text = $label
+        $category.HelpButton.ToolTip = Get-Translation -Key 'TweaksCategoryHelpTooltip' -FormatArgs @($label)
+    }
+    foreach ($name in $script:UiControlMappings.Keys) {
+        $mapping = $script:UiControlMappings[$name]
+        $control = $Window.FindName($name)
+        if (-not $control) { continue }
+        $text = Get-TweakControlText -Mapping $mapping
+        if ($mapping.Type -eq 'group') {
+            # Update item contents, keeping item identity and SelectedIndex unchanged.
+            for ($i = 0; $i -lt $text.Options.Count; $i++) {
+                $control.Items[$i].Content = $text.Options[$i]
+            }
+        }
+        $control.SetValue([System.Windows.Automation.AutomationProperties]::NameProperty, $text.Label)
+        if ($control -is [System.Windows.Controls.CheckBox]) { $control.Content = $text.Label }
+        else { $Window.FindName("${name}_LabelBorder").Child.Text = $text.Label }
+        # Label borders share this tooltip TextBlock with their combobox.
+        if ($control.ToolTip -is [System.Windows.Controls.TextBlock]) { $control.ToolTip.Text = $text.ToolTip }
+    }
+    Update-FeatureLabelLookup
+}
+
+<#
+    .SYNOPSIS
+        Refreshes localized app text and preset tooltips.
+
+    .DESCRIPTION
+        Updates app details, accessibility labels, and preset tooltips for the active language
+        while preserving app selections.
+
+    .PARAMETER AppsPanel
+        The panel containing the app selection controls.
+#>
+function Update-MainWindowAppLanguage {
+    param([System.Windows.Controls.Panel]$AppsPanel)
+
+    foreach ($app in $AppsPanel.Children) {
+        if ($app -isnot [System.Windows.Controls.CheckBox]) { continue }
+        $primaryAppId = @($app.AppIds)[0]
+        $app.AppName = Get-Translation -Key $primaryAppId -Field 'FriendlyName' -Section 'Apps'
+        $app.AppDescription = Get-Translation -Key $primaryAppId -Field 'Description' -Section 'Apps'
+        $app.AppNameText.Text = $app.AppName
+        $app.AppDescriptionText.Text = $app.AppDescription
+        $app.AppDescriptionText.ToolTip = $app.AppDescription
+        $app.SetValue([System.Windows.Automation.AutomationProperties]::NameProperty, $app.AppName)
+    }
+    foreach ($preset in $script:JsonPresetCheckboxes) {
+        $preset.ToolTip = Get-Translation -Key 'AppPresetSelectTooltip' -FormatArgs @($preset.Content)
+    }
+    # A future installed-only toggle must not consume a catalog in the old language.
+    $script:PreloadedAppData = $null
+}
+
+<#
+    .SYNOPSIS
+        Applies the current language to an existing main window.
+
+    .DESCRIPTION
+        Updates the interface and search results for the active language while preserving
+        user selections and app scroll position.
+
+    .PARAMETER Window
+        The initialized main window to refresh.
+#>
+function Update-MainWindowLanguage {
+    param([System.Windows.Window]$Window)
+
+    $appsPanel = $Window.FindName('AppSelectionPanel')
+    $appsScroll = Find-ParentScrollViewer -Element $appsPanel
+    $appOffset = if ($appsScroll) { $appsScroll.VerticalOffset } else { 0 }
+    $activeMatch = if ($script:AppSearchMatchIndex -ge 0 -and $script:AppSearchMatchIndex -lt $script:AppSearchMatches.Count) {
+        $script:AppSearchMatches[$script:AppSearchMatchIndex]
+    }
+
+    Update-WindowLanguageResources -Window $Window
+    Update-MainWindowTweakLanguage -Window $Window
+    Update-MainWindowAppLanguage -AppsPanel $appsPanel
+
+    $userCombo = $Window.FindName('UserSelectionCombo')
+    $userCombo.Items[0].Content = Get-Translation -Key 'HomeCurrentUserWithName' -FormatArgs @(Get-UserName)
+    Update-UserSelectionDescription -Window $Window -UserSelectionCombo $userCombo -OtherUsernameTextBox $Window.FindName('OtherUsernameTextBox') -UserSelectionDescription $Window.FindName('UserSelectionDescription')
+    Update-AppSelectionStatus -AppsPanel $appsPanel -AppSelectionStatus $Window.FindName('AppSelectionStatus') -AppRemovalScopeCombo $Window.FindName('AppRemovalScopeCombo') -AppRemovalScopeSection $Window.FindName('AppRemovalScopeSection') -AppRemovalScopeDescription $Window.FindName('AppRemovalScopeDescription') -UserSelectionCombo $userCombo
+    $validationMessage = $Window.FindName('UsernameValidationMessage')
+    if ($validationMessage.Text) {
+        Test-OtherUsername -Window $Window -UserSelectionCombo $userCombo -OtherUsernameTextBox $Window.FindName('OtherUsernameTextBox') -UsernameValidationMessage $validationMessage -AppRemovalScopeCombo $Window.FindName('AppRemovalScopeCombo') | Out-Null
+    }
+
+    Update-AppsPanelSort -AppsPanel $appsPanel -SortArrowName $Window.FindName('SortArrowName') -SortArrowDescription $Window.FindName('SortArrowDescription') -SortArrowAppId $Window.FindName('SortArrowAppId')
+    # Rerun matching against the translated labels without moving the user's viewport.
+    $script:UpdatingLanguage = $true
+    try {
+        foreach ($name in @('AppSearchBox', 'TweakSearchBox')) {
+            $Window.FindName($name).RaiseEvent([System.Windows.Controls.TextChangedEventArgs]::new([System.Windows.Controls.TextBox]::TextChangedEvent, [System.Windows.Controls.UndoAction]::None))
+        }
+    }
+    finally { $script:UpdatingLanguage = $false }
+    $activeIndex = [array]::IndexOf($script:AppSearchMatches, $activeMatch)
+    if ($activeIndex -ge 0) {
+        $script:AppSearchMatches[0].SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightColor')
+        $activeMatch.SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightActiveColor')
+        $script:AppSearchMatchIndex = $activeIndex
+    }
+    if ($appsScroll) { $appsScroll.ScrollToVerticalOffset($appOffset) }
+    Hide-Bubble -Immediate
+}
diff --git a/Scripts/GUI/MainWindow-TweaksBuilder.ps1 b/Scripts/GUI/MainWindow-TweaksBuilder.ps1
index 146c02f..1000248 100644
--- a/Scripts/GUI/MainWindow-TweaksBuilder.ps1
+++ b/Scripts/GUI/MainWindow-TweaksBuilder.ps1
@@ -1,6 +1,77 @@
 # MainWindow-TweaksBuilder.ps1
 # Dynamic tweaks UI construction from Features.json, tweak state management, selection clear, and search/highlight.
 
+<#
+    .SYNOPSIS
+        Resolves localized labels, tooltips, and options for a tweak control.
+
+    .DESCRIPTION
+        Provides consistent text for individual features and groups during control creation
+        and language changes.
+
+    .PARAMETER Mapping
+        A control mapping with Type and either FeatureId or GroupId and Values. Group values
+        contain FeatureIds and fallback Label text.
+
+    .PARAMETER Features
+        The feature definitions keyed by FeatureId. Defaults to $script:Features.
+
+    .OUTPUTS
+        PSCustomObject. Label, ToolTip, and Options, beginning with the No Change option.
+#>
+function Get-TweakControlText {
+    param(
+        [hashtable]$Mapping,
+        [hashtable]$Features = $script:Features
+    )
+
+    $options = @((Get-Translation -Key 'TweaksOptionNoChange'))
+    if ($Mapping.Type -eq 'group') {
+        $label = Get-Translation -Key $Mapping.GroupId -Field 'Label' -Section 'UiGroups'
+        $tooltip = Get-Translation -Key $Mapping.GroupId -Field 'ToolTip' -Section 'UiGroups'
+        $options += @($Mapping.Values | ForEach-Object {
+            Get-GroupValueTranslation -GroupId $Mapping.GroupId -FeatureId $_.FeatureIds[0] -FallbackLabel $_.Label
+        })
+    }
+    else {
+        $feature = $Features[$Mapping.FeatureId]
+        $label = Get-Translation -Key $Mapping.FeatureId -Field 'Label' -Section 'Features'
+        $tooltip = if ($feature.DisableWhenApplied -eq $true) {
+            Get-Translation -Key 'TweaksAlreadyAppliedTooltip'
+        }
+        else { Get-Translation -Key $Mapping.FeatureId -Field 'ToolTip' -Section 'Features' }
+        $optionKey = if ($Mapping.FeatureId -match '^Disable') { 'TweaksOptionDisable' }
+            elseif ($Mapping.FeatureId -match '^Enable') { 'TweaksOptionEnable' }
+            else { 'TweaksOptionApply' }
+        $options += Get-Translation -Key $optionKey
+    }
+
+    return [PSCustomObject]@{ Label = $label; ToolTip = $tooltip; Options = $options }
+}
+
+<#
+    .SYNOPSIS
+        Rebuilds localized feature and undo label lookups.
+
+    .DESCRIPTION
+        Keeps feature names used in change overviews in sync with the active language.
+
+    .PARAMETER Features
+        The feature definitions to translate. Defaults to the values of $script:Features.
+#>
+function Update-FeatureLabelLookup {
+    param([object[]]$Features = @($script:Features.Values))
+
+    $script:FeatureLabelLookup = @{}
+    $script:UndoFeatureLabelLookup = @{}
+    foreach ($feature in $Features) {
+        $script:FeatureLabelLookup[$feature.FeatureId] = Get-Translation -Key $feature.FeatureId -Field 'Label' -Section 'Features'
+        if ($feature.UndoLabel) {
+            $script:UndoFeatureLabelLookup[$feature.FeatureId] = Get-Translation -Key $feature.FeatureId -Field 'UndoLabel' -Section 'Features'
+        }
+    }
+}
+
 <#
     .SYNOPSIS
         Builds the main window's dynamic tweak controls from Features.json.
@@ -39,6 +110,7 @@ function New-DynamicTweakControls {
 
     $script:UiControlMappings = @{}
     $script:CategoryCardMap = @{}
+    $script:CategoryLanguageControls = @()
     $script:TweaksCompactMode = $null
     $script:TweaksCardsMovedFromCol2 = @()
 
@@ -128,6 +200,56 @@ function New-DynamicTweakControls {
         return $combo
     }
 
+    <#
+        .SYNOPSIS
+            Attaches a wrapping tooltip to a tweak control and its label border.
+
+        .PARAMETER Control
+            The tweak control receiving the tooltip.
+
+        .PARAMETER TooltipText
+            The localized text displayed by the tooltip.
+
+        .PARAMETER ShowOnDisabled
+            Enables tooltip display even when the tweak control is disabled.
+    #>
+    function Set-TweakControlToolTip($control, $tooltipText, [switch]$ShowOnDisabled) {
+        $tipBlock = New-Object System.Windows.Controls.TextBlock
+        $tipBlock.Text = $tooltipText
+        $tipBlock.TextWrapping = 'Wrap'
+        $tipBlock.MaxWidth = 420
+        $control.ToolTip = $tipBlock
+        if ($ShowOnDisabled) {
+            [System.Windows.Controls.ToolTipService]::SetShowOnDisabled($control, $true)
+        }
+        $labelBorder = $Window.FindName("$($control.Name)_LabelBorder")
+        if ($labelBorder) { $labelBorder.ToolTip = $tipBlock }
+    }
+
+    <#
+        .SYNOPSIS
+            Creates and maps a localized control for an individual feature.
+
+        .PARAMETER Feature
+            The feature definition to display.
+
+        .PARAMETER Parent
+            The category panel that receives the generated control.
+
+        .PARAMETER CategoryId
+            The category identifier stored in the control mapping.
+    #>
+    function Add-FeatureTweakControl($feature, $parent, $categoryId) {
+        $mapping = @{ Type = 'feature'; FeatureId = $feature.FeatureId; CategoryId = $categoryId }
+        $text = Get-TweakControlText -Mapping $mapping -Features $featureMap
+        $controlName = ("Feature_{0}_Combo" -f $feature.FeatureId) -replace '[^a-zA-Z0-9_]', ''
+        $control = New-LabeledCombo -parent $parent -labelText $text.Label -comboName $controlName -items $text.Options
+        if ($feature.ToolTip -or $feature.DisableWhenApplied -eq $true) {
+            Set-TweakControlToolTip -control $control -tooltipText $text.ToolTip -ShowOnDisabled
+        }
+        $script:UiControlMappings[$controlName] = $mapping
+    }
+
     <#
         .SYNOPSIS
             Returns the Features wiki URL for a tweak category.
@@ -213,6 +335,7 @@ function New-DynamicTweakControls {
                 if ($button.Tag) { Start-Process $button.Tag }
             })
         $headerRow.Children.Add($helpBtn) | Out-Null
+        $script:CategoryLanguageControls += @{ CategoryId = $categoryObj.CategoryId; Header = $header; HelpButton = $helpBtn }
 
         $panel.Children.Add($headerRow) | Out-Null
 
@@ -348,93 +471,31 @@ function New-DynamicTweakControls {
                     $soleFid = $featureIds[0]
 
                     if ($featureMap.ContainsKey($soleFid)) {
-                        $soleFeature = $featureMap[$soleFid]
-                        $soleFeatureLabel = Get-Translation -Key $soleFeature.FeatureId -Field 'Label' -Section 'Features'
-                        $opt = Get-Translation -Key 'TweaksOptionApply'
-                        if ($soleFeature.FeatureId -match '^Disable') { $opt = Get-Translation -Key 'TweaksOptionDisable' } elseif ($soleFeature.FeatureId -match '^Enable') { $opt = Get-Translation -Key 'TweaksOptionEnable' }
-                        $items = @((Get-Translation -Key 'TweaksOptionNoChange'), $opt)
-                        $comboName = ("Feature_{0}_Combo" -f $soleFeature.FeatureId) -replace '[^a-zA-Z0-9_]', ''
                         if (-not $panel) { $panel = Get-OrCreateCategoryCard -categoryObj $categoryObj }
-                        $combo = New-LabeledCombo -parent $panel -labelText $soleFeatureLabel -comboName $comboName -items $items
-                        # attach tooltip from Features.json if present
-                        if ($soleFeature.ToolTip -or $soleFeature.DisableWhenApplied -eq $true) {
-                            $tooltipText = Get-Translation -Key $soleFeature.FeatureId -Field 'ToolTip' -Section 'Features'
-                            if ($soleFeature.DisableWhenApplied -eq $true) {
-                                $tooltipText = Get-Translation -Key 'TweaksAlreadyAppliedTooltip'
-                            }
-                            $tipBlock = New-Object System.Windows.Controls.TextBlock
-                            $tipBlock.Text = $tooltipText
-                            $tipBlock.TextWrapping = 'Wrap'
-                            $tipBlock.MaxWidth = 420
-                            $combo.ToolTip = $tipBlock
-                            [System.Windows.Controls.ToolTipService]::SetShowOnDisabled($combo, $true)
-                            $lblBorderObj = $null
-                            try { $lblBorderObj = $Window.FindName("$comboName`_LabelBorder") } catch {}
-                            if ($lblBorderObj) { $lblBorderObj.ToolTip = $tipBlock }
-                        }
-                        $script:UiControlMappings[$comboName] = @{ Type = 'feature'; FeatureId = $soleFeature.FeatureId; Label = $soleFeatureLabel; CategoryId = $categoryId }
+                        Add-FeatureTweakControl -feature $featureMap[$soleFid] -parent $panel -categoryId $categoryId
                     }
                     continue
                 }
 
-                $groupLabel = Get-Translation -Key $group.GroupId -Field 'Label' -Section 'UiGroups'
-                $items = @((Get-Translation -Key 'TweaksOptionNoChange')) + ($filteredValues | ForEach-Object { Get-GroupValueTranslation -GroupId $group.GroupId -FeatureId $_.FeatureIds[0] -FallbackLabel $_.Label })
+                $mapping = @{ Type = 'group'; GroupId = $group.GroupId; Values = $filteredValues; CategoryId = $categoryId }
+                $text = Get-TweakControlText -Mapping $mapping -Features $featureMap
                 $comboName = 'Group_{0}Combo' -f $group.GroupId
                 if (-not $panel) { $panel = Get-OrCreateCategoryCard -categoryObj $categoryObj }
-                $combo = New-LabeledCombo -parent $panel -labelText $groupLabel -comboName $comboName -items $items
-                # attach tooltip from UiGroups if present
+                $combo = New-LabeledCombo -parent $panel -labelText $text.Label -comboName $comboName -items $text.Options
                 if ($group.ToolTip) {
-                    $tipBlock = New-Object System.Windows.Controls.TextBlock
-                    $tipBlock.Text = Get-Translation -Key $group.GroupId -Field 'ToolTip' -Section 'UiGroups'
-                    $tipBlock.TextWrapping = 'Wrap'
-                    $tipBlock.MaxWidth = 420
-                    $combo.ToolTip = $tipBlock
-                    $lblBorderObj = $null
-                    try { $lblBorderObj = $Window.FindName("$comboName`_LabelBorder") } catch {}
-                    if ($lblBorderObj) { $lblBorderObj.ToolTip = $tipBlock }
+                    Set-TweakControlToolTip -control $combo -tooltipText $text.ToolTip
                 }
-                $script:UiControlMappings[$comboName] = @{ Type = 'group'; Values = $filteredValues; Label = $groupLabel; CategoryId = $categoryId }
+                $script:UiControlMappings[$comboName] = $mapping
             }
             elseif ($item.Type -eq 'feature') {
-                $feature = $item.Data
-                $featureLabel = Get-Translation -Key $feature.FeatureId -Field 'Label' -Section 'Features'
-                $opt = Get-Translation -Key 'TweaksOptionApply'
-                if ($feature.FeatureId -match '^Disable') { $opt = Get-Translation -Key 'TweaksOptionDisable' } elseif ($feature.FeatureId -match '^Enable') { $opt = Get-Translation -Key 'TweaksOptionEnable' }
-                $items = @((Get-Translation -Key 'TweaksOptionNoChange'), $opt)
-                $comboName = ("Feature_{0}_Combo" -f $feature.FeatureId) -replace '[^a-zA-Z0-9_]', ''
                 if (-not $panel) { $panel = Get-OrCreateCategoryCard -categoryObj $categoryObj }
-                $combo = New-LabeledCombo -parent $panel -labelText $featureLabel -comboName $comboName -items $items
-                # attach tooltip from Features.json if present, and include the disabled-state reason
-                if ($feature.ToolTip -or $feature.DisableWhenApplied -eq $true) {
-                    $tooltipText = Get-Translation -Key $feature.FeatureId -Field 'ToolTip' -Section 'Features'
-                    if ($feature.DisableWhenApplied -eq $true) {
-                        $tooltipText = Get-Translation -Key 'TweaksAlreadyAppliedTooltip'
-                    }
-
-                    $tipBlock = New-Object System.Windows.Controls.TextBlock
-                    $tipBlock.Text = $tooltipText
-                    $tipBlock.TextWrapping = 'Wrap'
-                    $tipBlock.MaxWidth = 420
-                    $combo.ToolTip = $tipBlock
-                    [System.Windows.Controls.ToolTipService]::SetShowOnDisabled($combo, $true)
-                    $lblBorderObj = $null
-                    try { $lblBorderObj = $Window.FindName("$comboName`_LabelBorder") } catch {}
-                    if ($lblBorderObj) { $lblBorderObj.ToolTip = $tipBlock }
-                }
-                $script:UiControlMappings[$comboName] = @{ Type = 'feature'; FeatureId = $feature.FeatureId; Label = $feature.Label; CategoryId = $categoryId }
+                Add-FeatureTweakControl -feature $item.Data -parent $panel -categoryId $categoryId
             }
         }
     }
 
-    # Build a feature-label lookup so GenerateOverview can resolve feature IDs without reloading JSON
-    $script:FeatureLabelLookup = @{}
-    $script:UndoFeatureLabelLookup = @{}
-    foreach ($f in $featuresJson.Features) {
-        $script:FeatureLabelLookup[$f.FeatureId] = Get-Translation -Key $f.FeatureId -Field 'Label' -Section 'Features'
-        if ($f.UndoLabel) {
-            $script:UndoFeatureLabelLookup[$f.FeatureId] = Get-Translation -Key $f.FeatureId -Field 'UndoLabel' -Section 'Features'
-        }
-    }
+    # Overview generation uses the same labels as language refresh.
+    Update-FeatureLabelLookup -Features $featuresJson.Features
 }
 
 function Update-CurrentTweakSystemState {
diff --git a/Scripts/GUI/Set-WindowThemeResources.ps1 b/Scripts/GUI/Set-WindowThemeResources.ps1
index 8d6ec47..bf7c93e 100644
--- a/Scripts/GUI/Set-WindowThemeResources.ps1
+++ b/Scripts/GUI/Set-WindowThemeResources.ps1
@@ -113,6 +113,7 @@ function Set-WindowThemeResources {
     }
 
     $Theme = if ($usesDarkMode) { 'Dark' } else { 'Light' }
+    $window.Resources['AppUsesDarkMode'] = $usesDarkMode
 
     foreach ($Group in $ThemeColor.GetEnumerator()) {
         foreach ($Resource in $Group.Value.GetEnumerator()) {
@@ -130,12 +131,13 @@ function Set-WindowThemeResources {
     $window.Resources['AppIconFontFamily'] = [System.Windows.Media.FontFamily]::new($iconFontName)
 
     # Load and merge shared styles
-    if ($script:SharedStylesSchema -and (Test-Path $script:SharedStylesSchema)) {
+    if (-not $window.Resources.Contains('AppSharedStylesLoaded') -and $script:SharedStylesSchema -and (Test-Path $script:SharedStylesSchema)) {
         $sharedXaml = Get-Content -Path $script:SharedStylesSchema -Raw
         $sharedReader = [System.Xml.XmlReader]::Create([System.IO.StringReader]::new($sharedXaml))
         try {
             $sharedDict = [System.Windows.Markup.XamlReader]::Load($sharedReader)
             $window.Resources.MergedDictionaries.Add($sharedDict)
+            $window.Resources['AppSharedStylesLoaded'] = $true
         }
         finally {
             $sharedReader.Close()
diff --git a/Scripts/GUI/Show-AboutDialog.ps1 b/Scripts/GUI/Show-AboutDialog.ps1
index 133d2a6..5851fb8 100644
--- a/Scripts/GUI/Show-AboutDialog.ps1
+++ b/Scripts/GUI/Show-AboutDialog.ps1
@@ -13,7 +13,7 @@ function Show-AboutDialog {
     
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase | Out-Null
     
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
     
     # Determine owner window
     $ownerWindow = if ($Owner) { $Owner } else { $script:GuiWindow }
diff --git a/Scripts/GUI/Show-AppSelectionWindow.ps1 b/Scripts/GUI/Show-AppSelectionWindow.ps1
index b59d367..5dafba9 100644
--- a/Scripts/GUI/Show-AppSelectionWindow.ps1
+++ b/Scripts/GUI/Show-AppSelectionWindow.ps1
@@ -8,7 +8,7 @@
 function Show-AppSelectionWindow {
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase | Out-Null
 
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
     
     # Show overlay if main window exists
     $overlay = $null
diff --git a/Scripts/GUI/Show-ApplyModal.ps1 b/Scripts/GUI/Show-ApplyModal.ps1
index 89c7039..7ac62dd 100644
--- a/Scripts/GUI/Show-ApplyModal.ps1
+++ b/Scripts/GUI/Show-ApplyModal.ps1
@@ -18,7 +18,7 @@ function Show-ApplyModal {
     
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase | Out-Null
     
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
     
     # Determine owner window
     $ownerWindow = if ($Owner) { $Owner } else { $script:GuiWindow }
diff --git a/Scripts/GUI/Show-MainWindow.ps1 b/Scripts/GUI/Show-MainWindow.ps1
index 24d0ed8..5063957 100644
--- a/Scripts/GUI/Show-MainWindow.ps1
+++ b/Scripts/GUI/Show-MainWindow.ps1
@@ -3,14 +3,16 @@
         Creates and displays the main Win11Debloat window.
 #>
 function Show-MainWindow {
+    if (-not $script:Lang) { throw 'Unable to load UI language.' }
+    $script:CancelRequested = $false
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase,System.Windows.Forms | Out-Null
 
     $WinVersion = Get-ItemPropertyValue 'HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion' CurrentBuild
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
 
     # ---- Load XAML ----
     $xaml = Get-Content -Path $script:MainWindowSchema -Raw
-    $xaml = ConvertTo-LocalizedXaml -Xaml $xaml
+    $xaml = ConvertTo-LocalizedXaml -Xaml $xaml -DynamicResources
     $reader = [System.Xml.XmlReader]::Create([System.IO.StringReader]::new($xaml))
     try {
         $window = [System.Windows.Markup.XamlReader]::Load($reader)
@@ -20,6 +22,7 @@ function Show-MainWindow {
     }
 
     Set-WindowThemeResources -window $window -usesDarkMode $usesDarkMode
+    Update-WindowLanguageResources -Window $window
 
     $mainBorder = $window.FindName('MainBorder')
     $titleBarBackground = $window.FindName('TitleBarBackground')
@@ -46,12 +49,13 @@ function Show-MainWindow {
     $script:GuiWindow = $window
 
     # ---- Handle unhandled exceptions on the dispatcher thread ----
-    [System.Windows.Threading.Dispatcher]::CurrentDispatcher.Add_UnhandledException({
+    $dispatcherErrorHandler = [System.Windows.Threading.DispatcherUnhandledExceptionEventHandler]{
         param($sender, $e)
         Write-Warning "Unhandled exception in GUI: $($e.Exception.Message)"
         Write-Warning "Stack trace: $($e.Exception.StackTrace)"
         $e.Handled = $true
-    })
+    }
+    [System.Windows.Threading.Dispatcher]::CurrentDispatcher.Add_UnhandledException($dispatcherErrorHandler)
 
     # ---- Window chrome helpers ----
     $updateWindowChrome = { Update-MainWindowChrome -Window $window -MainBorder $mainBorder -TitleBarBackground $titleBarBackground -NormalWindowShadow $normalWindowShadow }
@@ -82,6 +86,7 @@ function Show-MainWindow {
 
     # ---- Menu/button event wiring ----
     $kofiBtn.Add_Click({ Start-Process "https://ko-fi.com/raphire" })
+    $window.FindName('SettingsBtn').Add_Click({ Open-MainWindowSettings -Window $window })
 
     $menuBtn.Add_Click({
         $menuBtn.ContextMenu.PlacementTarget = $menuBtn
@@ -167,7 +172,7 @@ function Show-MainWindow {
     # ---- Wire export/import ----
     $exportConfigBtn.Add_Click({
         try {
-            Export-Configuration -Owner $window -UsesDarkMode $usesDarkMode -AppsPanel $appsPanel -UiControlMappings $script:UiControlMappings -UserSelectionCombo $userSelectionCombo -OtherUsernameTextBox $otherUsernameTextBox
+            Export-Configuration -Owner $window -UsesDarkMode (Get-AppUsesDarkMode) -AppsPanel $appsPanel -UiControlMappings $script:UiControlMappings -UserSelectionCombo $userSelectionCombo -OtherUsernameTextBox $otherUsernameTextBox
         }
         catch {
             Write-Warning "Export configuration failed: $($_.Exception.Message)"
@@ -177,7 +182,7 @@ function Show-MainWindow {
 
     $importConfigBtn.Add_Click({
         try {
-            Import-Configuration -Owner $window -UsesDarkMode $usesDarkMode -AppsPanel $appsPanel -UiControlMappings $script:UiControlMappings -UserSelectionCombo $userSelectionCombo -OtherUsernameTextBox $otherUsernameTextBox -OnAppsImported { Update-AppSelectionStatus -AppsPanel $appsPanel -AppSelectionStatus $appSelectionStatus -AppRemovalScopeCombo $appRemovalScopeCombo -AppRemovalScopeSection $appRemovalScopeSection -AppRemovalScopeDescription $appRemovalScopeDescription -UserSelectionCombo $userSelectionCombo; Update-AppPresetStates -AppsPanel $appsPanel } -OnImportCompleted {
+            Import-Configuration -Owner $window -UsesDarkMode (Get-AppUsesDarkMode) -AppsPanel $appsPanel -UiControlMappings $script:UiControlMappings -UserSelectionCombo $userSelectionCombo -OtherUsernameTextBox $otherUsernameTextBox -OnAppsImported { Update-AppSelectionStatus -AppsPanel $appsPanel -AppSelectionStatus $appSelectionStatus -AppRemovalScopeCombo $appRemovalScopeCombo -AppRemovalScopeSection $appRemovalScopeSection -AppRemovalScopeDescription $appRemovalScopeDescription -UserSelectionCombo $userSelectionCombo; Update-AppPresetStates -AppsPanel $appsPanel } -OnImportCompleted {
                 $tabControl.SelectedIndex = 3
                 Update-NavigationButtons -Window $window -TabControl $tabControl
                 $window.Dispatcher.BeginInvoke([System.Windows.Threading.DispatcherPriority]::Loaded, [action]{
@@ -382,16 +387,14 @@ function Show-MainWindow {
 
         if ([string]::IsNullOrWhiteSpace($searchText)) { return }
 
-        $highlightBrush = $window.Resources["SearchHighlightColor"]
-        $activeHighlightBrush = $window.Resources["SearchHighlightActiveColor"]
-
+        # Keep existing highlights in sync when Auto changes the window's theme resources.
         foreach ($child in $appsPanel.Children) {
             if ($child -is [System.Windows.Controls.CheckBox] -and $child.Visibility -eq 'Visible') {
                 $appName = if ($child.AppName) { $child.AppName } else { '' }
                 $appId = if ($child.Tag) { $child.Tag.ToString() } else { '' }
                 $appDesc = if ($child.AppDescription) { $child.AppDescription } else { '' }
                 if ($appName.ToLower().Contains($searchText) -or $appId.ToLower().Contains($searchText) -or $appDesc.ToLower().Contains($searchText)) {
-                    $child.Background = $highlightBrush
+                    $child.SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightColor')
                     $script:AppSearchMatches += $child
                 }
             }
@@ -399,9 +402,9 @@ function Show-MainWindow {
 
         if ($script:AppSearchMatches.Count -gt 0) {
             $script:AppSearchMatchIndex = 0
-            $script:AppSearchMatches[0].Background = $activeHighlightBrush
+            $script:AppSearchMatches[0].SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightActiveColor')
             $scrollViewer = Find-ParentScrollViewer -Element $appsPanel
-            if ($scrollViewer) {
+            if ($scrollViewer -and -not $script:UpdatingLanguage) {
                 Scroll-ToItemIfNotVisible -ScrollViewer $scrollViewer -Item $script:AppSearchMatches[0] -Container $appsPanel
             }
         }
@@ -410,9 +413,9 @@ function Show-MainWindow {
     $appSearchBox.Add_KeyDown({
         param($sourceControl, $e)
         if ($e.Key -eq [System.Windows.Input.Key]::Enter -and $script:AppSearchMatches.Count -gt 0) {
-            $script:AppSearchMatches[$script:AppSearchMatchIndex].Background = $window.Resources["SearchHighlightColor"]
+            $script:AppSearchMatches[$script:AppSearchMatchIndex].SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightColor')
             $script:AppSearchMatchIndex = ($script:AppSearchMatchIndex + 1) % $script:AppSearchMatches.Count
-            $script:AppSearchMatches[$script:AppSearchMatchIndex].Background = $window.Resources["SearchHighlightActiveColor"]
+            $script:AppSearchMatches[$script:AppSearchMatchIndex].SetResourceReference([System.Windows.Controls.Control]::BackgroundProperty, 'SearchHighlightActiveColor')
             $scrollViewer = Find-ParentScrollViewer -Element $appsPanel
             if ($scrollViewer) {
                 Scroll-ToItemIfNotVisible -ScrollViewer $scrollViewer -Item $script:AppSearchMatches[$script:AppSearchMatchIndex] -Container $appsPanel
@@ -440,7 +443,6 @@ function Show-MainWindow {
         if ([string]::IsNullOrWhiteSpace($searchText)) { return }
 
         $firstMatch = $null
-        $highlightBrush = $window.Resources["SearchHighlightColor"]
         $col0 = $window.FindName('Column0Panel')
         $col1 = $window.FindName('Column1Panel')
         $col2 = $window.FindName('Column2Panel')
@@ -472,7 +474,13 @@ function Show-MainWindow {
                         }
 
                         if ($matchFound -and $controlToHighlight) {
-                            $controlToHighlight.Background = $highlightBrush
+                            $backgroundProperty = if ($controlToHighlight -is [System.Windows.Controls.Border]) {
+                                [System.Windows.Controls.Border]::BackgroundProperty
+                            }
+                            else {
+                                [System.Windows.Controls.Control]::BackgroundProperty
+                            }
+                            $controlToHighlight.SetResourceReference($backgroundProperty, 'SearchHighlightColor')
                             if ($null -eq $firstMatch) { $firstMatch = $controlToHighlight }
                         }
                     }
@@ -480,7 +488,7 @@ function Show-MainWindow {
             }
         }
 
-        if ($firstMatch -and $tweaksScrollViewer) {
+        if ($firstMatch -and $tweaksScrollViewer -and -not $script:UpdatingLanguage) {
             Scroll-ToItemIfNotVisible -ScrollViewer $tweaksScrollViewer -Item $firstMatch -Container $tweaksGrid
         }
     })
@@ -896,6 +904,10 @@ function Show-MainWindow {
     })
 
     $window.Show() | Out-Null
+    $themeTimer = [System.Windows.Threading.DispatcherTimer]::new()
+    $themeTimer.Interval = [TimeSpan]::FromSeconds(2)
+    $themeTimer.Add_Tick({ Update-AutoThemeResources -Window $window })
+    $themeTimer.Start()
 
     # If WhatIf mode is enabled, notify the user that no changes will be made
     if ($script:Params.ContainsKey("WhatIf")) {
@@ -904,6 +916,11 @@ function Show-MainWindow {
         }) | Out-Null
     }
 
-    [System.Windows.Threading.Dispatcher]::PushFrame($frame)
+    try { [System.Windows.Threading.Dispatcher]::PushFrame($frame) }
+    finally {
+        $themeTimer.Stop()
+        [System.Windows.Threading.Dispatcher]::CurrentDispatcher.Remove_UnhandledException($dispatcherErrorHandler)
+        if ($script:BubblePopup) { $script:BubblePopup.IsOpen = $false }
+    }
     return $null
 }
diff --git a/Scripts/GUI/Show-MessageBox.ps1 b/Scripts/GUI/Show-MessageBox.ps1
index cdce7b4..e43ac5a 100644
--- a/Scripts/GUI/Show-MessageBox.ps1
+++ b/Scripts/GUI/Show-MessageBox.ps1
@@ -36,7 +36,7 @@ function Show-MessageBox {
     
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase | Out-Null
     
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
     
     # Determine owner window - use provided Owner, or fall back to main GUI window
     $ownerWindow = if ($Owner) { $Owner } else { $script:GuiWindow }
diff --git a/Scripts/GUI/Show-RestoreBackupDialog.ps1 b/Scripts/GUI/Show-RestoreBackupDialog.ps1
index 6d62dca..790793c 100644
--- a/Scripts/GUI/Show-RestoreBackupDialog.ps1
+++ b/Scripts/GUI/Show-RestoreBackupDialog.ps1
@@ -26,7 +26,7 @@ function Show-RestoreBackupDialog {
 
     Add-Type -AssemblyName PresentationFramework,PresentationCore,WindowsBase | Out-Null
 
-    $usesDarkMode = Get-SystemUsesDarkMode
+    $usesDarkMode = Get-AppUsesDarkMode
     $ownerWindow = if ($Owner) { $Owner } else { $script:GuiWindow }
 
     $overlay = $null
diff --git a/Scripts/GUI/Show-SettingsDialog.ps1 b/Scripts/GUI/Show-SettingsDialog.ps1
new file mode 100644
index 0000000..9fb5986
--- /dev/null
+++ b/Scripts/GUI/Show-SettingsDialog.ps1
@@ -0,0 +1,92 @@
+<#
+    .SYNOPSIS
+        Shows the modal theme and language settings dialog.
+
+    .DESCRIPTION
+        Lets users choose a theme and language. Changes take effect only after Save;
+        closing without saving discards edits. Displays an error if saving fails.
+
+    .PARAMETER Owner
+        The window that owns the settings dialog.
+
+    .OUTPUTS
+        System.Boolean. $true when changed preferences were saved; $false when closed
+        without changes or without saving.
+#>
+function Show-SettingsDialog {
+    param([Parameter(Mandatory)][System.Windows.Window]$Owner)
+    $path = Join-Path (Split-Path $script:MainWindowSchema -Parent) 'SettingsWindow.xaml'
+    $xaml = ConvertTo-LocalizedXaml -Xaml (Get-Content -LiteralPath $path -Raw)
+    $reader = [System.Xml.XmlReader]::Create([System.IO.StringReader]::new($xaml))
+    try { $dialog = [System.Windows.Markup.XamlReader]::Load($reader) }
+    finally { $reader.Close() }
+    $dialog.Owner = $Owner
+    Set-WindowThemeResources -window $dialog -usesDarkMode (Get-AppUsesDarkMode)
+    $dialog.Tag = $false
+    $overlay = $Owner.FindName('ModalOverlay')
+    $languageCombo = $dialog.FindName('SettingsLanguageCombo')
+    $auto = [System.Windows.Controls.ComboBoxItem]::new()
+    $auto.Content = Get-Translation -Key 'SettingsLanguageAuto'
+    $auto.Tag = 'Auto'
+    [void]$languageCombo.Items.Add($auto)
+    foreach ($folder in (Get-AvailableLanguageFolders)) {
+        $item = [System.Windows.Controls.ComboBoxItem]::new()
+        try {
+            $culture = [System.Globalization.CultureInfo]::GetCultureInfo($folder.Name)
+            $name = $culture.NativeName
+            $item.Content = $culture.TextInfo.ToUpper($name.Substring(0, 1)) + $name.Substring(1)
+        }
+        catch { $item.Content = $folder.Name }
+        $item.Tag = $folder.Name
+        [void]$languageCombo.Items.Add($item)
+    }
+    foreach ($item in $languageCombo.Items) {
+        if ($item.Tag -eq $script:UiPreferences.Language) { $languageCombo.SelectedItem = $item; break }
+    }
+
+    # Event handlers share the pending value without changing saved preferences.
+    $pendingTheme = [ref]([string]$script:UiPreferences.Theme)
+    $savePreferences = {
+        $theme = $pendingTheme.Value
+        $language = [string]$languageCombo.SelectedItem.Tag
+        if ($theme -eq $script:UiPreferences.Theme -and $language -eq $script:UiPreferences.Language) { $dialog.Close(); return }
+        try {
+            $lang = if ($language -eq $script:UiPreferences.Language) { $script:Lang } else { Get-UiLanguage -Language $language }
+            if (-not $lang) { throw 'Unable to load language.' }
+            if ($language -ne 'Auto' -and $lang.LanguageCode -ne $language) { throw 'The selected language could not be loaded.' }
+            $preferences = @{ Theme = $theme; Language = $language }
+            Save-UiPreferences -Preferences $preferences
+            $script:UiPreferences = $preferences
+            $script:Lang = $lang
+            $dialog.Tag = $true
+            $dialog.Close()
+        }
+        catch {
+            $errorText = $dialog.FindName('SettingsErrorText')
+            $errorText.Text = Get-Translation -Key 'SettingsSaveError'
+            $errorText.Visibility = 'Visible'
+            Write-Warning "Unable to update UI preferences: $($_.Exception.Message)"
+        }
+    }
+    foreach ($mode in @('Auto', 'Light', 'Dark')) {
+        $button = $dialog.FindName("Theme${mode}Button")
+        if ($mode -eq $script:UiPreferences.Theme) { $button.SetResourceReference([System.Windows.FrameworkElement]::StyleProperty, 'PrimaryButtonStyle') }
+        $button.Add_Click({
+            param($sender, $e)
+            $pendingTheme.Value = [string]$sender.Tag
+            foreach ($themeMode in @('Auto', 'Light', 'Dark')) {
+                $style = if ($themeMode -eq $pendingTheme.Value) { 'PrimaryButtonStyle' } else { 'SecondaryButtonStyle' }
+                $dialog.FindName("Theme${themeMode}Button").SetResourceReference([System.Windows.FrameworkElement]::StyleProperty, $style)
+            }
+        })
+    }
+    $dialog.FindName('SaveButton').Add_Click($savePreferences)
+    $dialog.FindName('TitleBar').Add_MouseLeftButtonDown({ $dialog.DragMove() })
+    $dialog.FindName('CloseBtn').Add_Click({ $dialog.Close() })
+    try {
+        if ($overlay) { $overlay.Visibility = 'Visible' }
+        [void]$dialog.ShowDialog()
+        return [bool]$dialog.Tag
+    }
+    finally { if ($overlay) { $overlay.Visibility = 'Collapsed' } }
+}
diff --git a/Scripts/GUI/Ui-Preferences.ps1 b/Scripts/GUI/Ui-Preferences.ps1
new file mode 100644
index 0000000..df5f300
--- /dev/null
+++ b/Scripts/GUI/Ui-Preferences.ps1
@@ -0,0 +1,157 @@
+<#
+    .SYNOPSIS
+        Reads saved UI theme and language preferences.
+
+    .DESCRIPTION
+        Uses Auto when no valid saved theme or language preference is available.
+        UI preferences are separate from exported debloat configurations.
+
+    .PARAMETER Path
+        The preferences JSON file. Defaults to $script:UiPreferencesFilePath.
+
+    .OUTPUTS
+        System.Collections.Hashtable. Theme and Language preference values.
+#>
+function Get-UiPreferences {
+    param([string]$Path = $script:UiPreferencesFilePath)
+    $preferences = @{ Theme = 'Auto'; Language = 'Auto' }
+    if (Test-Path -LiteralPath $Path) {
+        try {
+            $saved = Get-Content -LiteralPath $Path -Raw -Encoding UTF8 | ConvertFrom-Json
+            if ($saved.Theme -in @('Auto', 'Light', 'Dark')) { $preferences.Theme = $saved.Theme }
+            if ($saved.Language -eq 'Auto' -or $saved.Language -match '^[a-zA-Z]{2,3}(-[a-zA-Z0-9]{2,8})+$') {
+                $preferences.Language = $saved.Language
+            }
+        }
+        catch { Write-Warning "Unable to read UI preferences: $($_.Exception.Message)" }
+    }
+    return $preferences
+}
+
+<#
+    .SYNOPSIS
+        Saves UI preferences to a JSON file.
+
+    .PARAMETER Preferences
+        The Theme and Language preferences to save.
+
+    .PARAMETER Path
+        The destination JSON file. Defaults to $script:UiPreferencesFilePath.
+#>
+function Save-UiPreferences {
+    param(
+        [Parameter(Mandatory)]$Preferences,
+        [string]$Path = $script:UiPreferencesFilePath
+    )
+    $directory = Split-Path -Parent $Path
+    [void][System.IO.Directory]::CreateDirectory($directory)
+    $temporaryPath = "$Path.tmp"
+    try {
+        $Preferences | ConvertTo-Json | Set-Content -LiteralPath $temporaryPath -Encoding UTF8 -ErrorAction Stop
+        Move-Item -LiteralPath $temporaryPath -Destination $Path -Force -ErrorAction Stop
+    }
+    finally {
+        if (Test-Path -LiteralPath $temporaryPath) { Remove-Item -LiteralPath $temporaryPath -Force }
+    }
+}
+
+<#
+    .SYNOPSIS
+        Resolves the application's effective dark mode setting.
+
+    .DESCRIPTION
+        Uses the selected Light or Dark theme, or follows the Windows app theme in Auto mode.
+
+    .OUTPUTS
+        System.Boolean. Whether the application should use dark mode.
+#>
+function Get-AppUsesDarkMode {
+    switch ($script:UiPreferences.Theme) {
+        'Light' { return $false }
+        'Dark' { return $true }
+        default { return (Get-SystemUsesDarkMode) }
+    }
+}
+
+<#
+    .SYNOPSIS
+        Loads the language selected by a UI preference.
+
+    .DESCRIPTION
+        Auto follows the current UI culture. Resolves the requested language to an available
+        translation, falling back to English when needed.
+
+    .PARAMETER Language
+        Auto to use the current UI culture, or a language code such as nl-NL.
+
+    .OUTPUTS
+        PSCustomObject. The loaded language content, or $null when loading fails.
+#>
+function Get-UiLanguage {
+    param([string]$Language)
+    if ($Language -eq 'Auto') { return (Import-LanguageFile) }
+    return (Import-LanguageFile -LanguageCode $Language)
+}
+
+<#
+    .SYNOPSIS
+        Initializes UI preferences and the active language.
+
+    .DESCRIPTION
+        Loads saved preferences and resolves the startup language, allowing an explicit
+        language choice to override the saved preference.
+
+    .PARAMETER Language
+        An optional language preference override, including Auto. When omitted or empty,
+        uses the saved language preference.
+#>
+function Initialize-UiPreferences {
+    param([string]$Language)
+
+    $script:UiPreferences = Get-UiPreferences
+    if ($Language) { $script:UiPreferences.Language = $Language }
+    $script:Lang = Get-UiLanguage -Language $script:UiPreferences.Language
+    if ($script:Lang -and $script:UiPreferences.Language -ne 'Auto') {
+        $script:UiPreferences.Language = $script:Lang.LanguageCode
+    }
+}
+
+<#
+    .SYNOPSIS
+        Refreshes window themes when the application follows the Windows theme.
+
+    .DESCRIPTION
+        Keeps the window and its owned dialogs in sync with the Windows app theme when
+        Auto is selected.
+
+    .PARAMETER Window
+        The window to check, along with its owned windows.
+#>
+function Update-AutoThemeResources {
+    param([System.Windows.Window]$Window)
+    if ($script:UiPreferences.Theme -ne 'Auto') { return }
+    $dark = Get-SystemUsesDarkMode
+    if ($Window.Resources['AppUsesDarkMode'] -ne $dark) {
+        Set-WindowThemeResources -window $Window -usesDarkMode $dark
+    }
+    foreach ($owned in $Window.OwnedWindows) { Update-AutoThemeResources -Window $owned }
+}
+
+<#
+    .SYNOPSIS
+        Opens settings and applies saved presentation changes to the main window.
+
+    .PARAMETER Window
+        The main window that owns the settings dialog and receives saved changes.
+#>
+function Open-MainWindowSettings {
+    param([System.Windows.Window]$Window)
+    if ($script:IsLoadingApps) { return }
+    $previousLanguageCode = $script:Lang.LanguageCode
+    if (Show-SettingsDialog -Owner $Window) {
+        Set-WindowThemeResources -window $Window -usesDarkMode (Get-AppUsesDarkMode)
+        if ($script:Lang.LanguageCode -ne $previousLanguageCode) {
+            Update-MainWindowLanguage -Window $Window
+        }
+    }
+}
diff --git a/Tests/Import-LanguageFile.Tests.ps1 b/Tests/Import-LanguageFile.Tests.ps1
index c31291c..55c9fd1 100644
--- a/Tests/Import-LanguageFile.Tests.ps1
+++ b/Tests/Import-LanguageFile.Tests.ps1
@@ -4,6 +4,26 @@ BeforeAll {
     $script:LanguagesPath = Join-Path $PSScriptRoot 'TestData\LanguageLoading'
 }
 
+Describe 'Get-AvailableLanguageFolders' {
+    It 'lists complete folders in name order' {
+        @(Get-AvailableLanguageFolders | Select-Object -ExpandProperty Name) | Should -Be @('en-US', 'es-ES')
+    }
+
+    It 'excludes folders with a missing catalog or a directory in place of a catalog' {
+        $languagesPath = Join-Path $TestDrive 'Discovery'
+        New-Item -ItemType Directory -Path $languagesPath | Out-Null
+        foreach ($name in @('complete', 'missing', 'directory')) {
+            Copy-Item -LiteralPath (Join-Path $script:LanguagesPath 'en-US') -Destination (Join-Path $languagesPath $name) -Recurse
+        }
+        Remove-Item -LiteralPath (Join-Path $languagesPath 'missing/Apps.json')
+        Remove-Item -LiteralPath (Join-Path $languagesPath 'directory/Apps.json')
+        New-Item -ItemType Directory -Path (Join-Path $languagesPath 'directory/Apps.json') | Out-Null
+
+        @(Get-AvailableLanguageFolders -LanguagesPath $languagesPath | Select-Object -ExpandProperty Name) | Should -Be @('complete')
+        (Import-LanguageContent -LanguageFolder 'complete' -LanguagesPath $languagesPath).Apps.'TestApp.One'.FriendlyName | Should -Be 'Test App'
+    }
+}
+
 Describe 'Resolve-LanguageFolder' {
     It 'resolves <Case>' -ForEach @(
         @{ Case = 'an exact match'; LanguageCode = 'en-US'; Expected = 'en-US' }
@@ -259,4 +279,12 @@ Describe 'ConvertTo-LocalizedXaml' {
 
         { ConvertTo-LocalizedXaml -Xaml $xaml -Lang $script:EnLang } | Should -Throw '*DisableTelemetry*'
     }
+
+    It 'emits live resource references while retaining missing-key and fallback validation' {
+        $xaml = '<Button Content="%LANG:TitleBarOptions%"/>'
+        ConvertTo-LocalizedXaml -Xaml $xaml -Lang $script:EsLang -DynamicResources |
+            Should -Be '<Button Content="{DynamicResource Language_TitleBarOptions}"/>'
+        { ConvertTo-LocalizedXaml -Xaml '<Button Content="%LANG:MissingKey%"/>' -Lang $script:EnLang -DynamicResources } |
+            Should -Throw '*MissingKey*'
+    }
 }
diff --git a/Tests/MainWindow-Deployment.Tests.ps1 b/Tests/MainWindow-Deployment.Tests.ps1
index 4217237..fced2bb 100644
--- a/Tests/MainWindow-Deployment.Tests.ps1
+++ b/Tests/MainWindow-Deployment.Tests.ps1
@@ -64,6 +64,21 @@ Describe 'Get-UndoFeatureLabel' {
         Mock Get-ItemProperty { throw 'Registry unavailable' }
         Get-SystemUsesDarkMode | Should -BeFalse
     }
+
+    It 'quietly falls back to light mode on repeated missing personalization lookups' {
+        $ErrorActionPreference = 'Continue'
+        Mock Get-ItemProperty {
+            param($ErrorAction)
+            $lookupErrorAction = if ($ErrorAction) { $ErrorAction } else { 'Continue' }
+            Write-Error -Message 'Personalization key was not found.' -Category ObjectNotFound -ErrorAction $lookupErrorAction
+        }
+
+        foreach ($poll in 1..3) {
+            $output = @(Get-SystemUsesDarkMode *>&1)
+            $output.Count | Should -Be 1
+            $output[0] | Should -BeFalse
+        }
+    }
 }
 
 Describe 'Test-OtherUsername' {
diff --git a/Tests/MainWindow-Localization.Tests.ps1 b/Tests/MainWindow-Localization.Tests.ps1
new file mode 100644
index 0000000..6956cd7
--- /dev/null
+++ b/Tests/MainWindow-Localization.Tests.ps1
@@ -0,0 +1,310 @@
+# Headless component tests: no main/settings XAML, Show/ShowDialog, or message loop.
+BeforeAll {
+    Add-Type -AssemblyName PresentationFramework
+    $script:RepoRoot = Split-Path $PSScriptRoot -Parent
+    foreach ($file in @('FileIO/Import-JsonFile', 'FileIO/Import-LanguageFile',
+        'GUI/Ui-Preferences', 'GUI/Show-SettingsDialog', 'GUI/Set-WindowThemeResources',
+        'GUI/MainWindow-Localization', 'GUI/MainWindow-TweaksBuilder', 'GUI/MainWindow-AppSelection',
+        'GUI/MainWindow-Deployment', 'GUI/Show-Bubble', 'Helpers/Get-UserName')) {
+        . "$script:RepoRoot/Scripts/$file.ps1"
+    }
+    $script:LanguagesPath = Join-Path $script:RepoRoot 'Config/Languages'
+    $script:FeaturesFilePath = Join-Path $script:RepoRoot 'Config/Features.json'
+    $script:Features = @{}
+    foreach ($feature in (Import-JsonFile -filePath $script:FeaturesFilePath).Features) { $script:Features[$feature.FeatureId] = $feature }
+    $tokens = $null; $parseErrors = $null
+    $mainAst = [System.Management.Automation.Language.Parser]::ParseFile("$script:RepoRoot/Scripts/GUI/Show-MainWindow.ps1", [ref]$tokens, [ref]$parseErrors)
+    $script:SearchHandlers = @{}
+    foreach ($handler in $mainAst.FindAll({
+        param($node)
+        $node -is [System.Management.Automation.Language.InvokeMemberExpressionAst] -and
+        $node.Member.Value -eq 'Add_TextChanged' -and $node.Expression.VariablePath.UserPath -in @('appSearchBox', 'tweakSearchBox')
+    }, $true)) {
+        $script:SearchHandlers[$handler.Expression.VariablePath.UserPath] = $handler.Arguments[0].ScriptBlock.GetScriptBlock()
+    }
+
+    <#
+        .SYNOPSIS
+            Creates a minimal window for dynamic tweak localization tests.
+
+        .OUTPUTS
+            System.Windows.Window. The test window with its registered column panels.
+    #>
+    function New-LanguageTestWindow {
+        $window = [System.Windows.Window]::new()
+        [System.Windows.NameScope]::SetNameScope($window, [System.Windows.NameScope]::new())
+        $window.Content = [System.Windows.Controls.StackPanel]::new()
+        foreach ($name in @('Column0Panel', 'Column1Panel', 'Column2Panel')) {
+            $panel = [System.Windows.Controls.StackPanel]::new()
+            $window.RegisterName($name, $panel)
+            [void]$window.Content.Children.Add($panel)
+        }
+        return $window
+    }
+}
+
+Describe 'Language changes on existing controls' {
+    BeforeEach {
+        $script:Lang = Import-LanguageFile -LanguageCode 'en-US'
+        $script:ModernStandbySupported = $false
+    }
+
+    It 'matches fresh and refreshed tweak text on Windows build <Build>' -ForEach @(
+        @{ Build = 19045 }
+        @{ Build = 26100 }
+    ) {
+        <#
+            .SYNOPSIS
+                Serializes current tweak presentation text for comparison.
+
+            .DESCRIPTION
+                Captures labels, tooltips, and options to compare freshly created controls
+                with controls refreshed after a language change.
+
+            .PARAMETER Window
+                The test window containing registered tweak controls and label borders.
+
+            .OUTPUTS
+                System.String. The serialized presentation snapshot.
+        #>
+        function Get-TweakPresentationSnapshot($window) {
+            $rows = foreach ($name in ($script:UiControlMappings.Keys | Sort-Object)) {
+                $control = $window.FindName($name)
+                $label = if ($control -is [System.Windows.Controls.CheckBox]) { $control.Content }
+                    else { $window.FindName("${name}_LabelBorder").Child.Text }
+                [PSCustomObject]@{
+                    Name = $name
+                    Label = $label
+                    ToolTip = if ($control.ToolTip) { $control.ToolTip.Text } else { $null }
+                    Options = @($control.Items | ForEach-Object { $_.Content })
+                }
+            }
+            return ConvertTo-Json -InputObject @($rows) -Depth 4 -Compress
+        }
+
+        foreach ($language in @('nl-NL', 'pt-BR')) {
+            $script:Lang = Import-LanguageFile -LanguageCode $language
+            $fresh = New-LanguageTestWindow
+            New-DynamicTweakControls -Window $fresh -WinVersion $Build
+            $expected = Get-TweakPresentationSnapshot $fresh
+
+            $script:Lang = Import-LanguageFile -LanguageCode 'en-US'
+            $refreshed = New-LanguageTestWindow
+            New-DynamicTweakControls -Window $refreshed -WinVersion $Build
+            $script:Lang = Import-LanguageFile -LanguageCode $language
+            Update-MainWindowTweakLanguage -Window $refreshed
+            Get-TweakPresentationSnapshot $refreshed | Should -Be $expected
+        }
+    }
+
+    It 'updates text, accessibility names and detached menu resources with English fallback' {
+        $window = New-LanguageTestWindow
+        $button = [System.Windows.Controls.Button]::new()
+        $button.SetResourceReference([System.Windows.Controls.ContentControl]::ContentProperty, 'Language_SettingsTitle')
+        $button.SetResourceReference([System.Windows.Automation.AutomationProperties]::NameProperty, 'Language_SettingsTitle')
+        [void]$window.Content.Children.Add($button)
+        $menu = [System.Windows.Controls.ContextMenu]::new()
+        $window.RegisterName('MainMenu', $menu)
+        $item = [System.Windows.Controls.MenuItem]::new()
+        $item.SetResourceReference([System.Windows.Controls.HeaderedItemsControl]::HeaderProperty, 'Language_MenuAbout')
+        [void]$menu.Items.Add($item)
+
+        foreach ($language in @('en-US', 'nl-NL', 'pt-BR', 'en-US')) {
+            $script:Lang = Import-LanguageFile -LanguageCode $language
+            Update-WindowLanguageResources -Window $window
+            $button.Content | Should -Be (Get-Translation -Key 'SettingsTitle')
+            [System.Windows.Automation.AutomationProperties]::GetName($button) | Should -Be $button.Content
+            $item.Header | Should -Be (Get-Translation -Key 'MenuAbout')
+        }
+        $script:Lang = [PSCustomObject]@{ Chrome = [PSCustomObject]@{ SettingsTitle = 'Custom & <text>' }; Fallback = $script:Lang }
+        Update-WindowLanguageResources -Window $window
+        $button.Content | Should -Be 'Custom & <text>'
+        $item.Header | Should -Be 'About'
+    }
+
+    It 'translates generated tweaks without replacing controls, selections or applied-state metadata' {
+        $window = New-LanguageTestWindow
+        New-DynamicTweakControls -Window $window -WinVersion 26100
+        $checkbox = $window.FindName('Feature_DisableTelemetry_Combo')
+        $checkbox.IsChecked = $false
+        $checkbox | Add-Member -NotePropertyMembers @{ InitialState = $true; SystemState = $true }
+        $disabled = $window.FindName('Feature_DisableWidgets_Combo')
+        $disabled.IsChecked = $true
+        $disabled.IsEnabled = $false
+        $disabled | Add-Member -NotePropertyMembers @{ InitialState = $true; SystemState = $true; DisableWhenApplied = $true }
+        $group = $window.FindName('Group_SearchIconCombo')
+        $group.SelectedIndex = 2
+        $group | Add-Member -NotePropertyMembers @{ InitialIndex = 1; SystemIndex = 1 }
+        $selectedItem = $group.SelectedItem
+        $script:SelectionChanges = 0
+        $group.Add_SelectionChanged({ $script:SelectionChanges++ })
+        $before = @(Get-PendingTweakActions -Window $window -ShowAppliedTweaksMode $true | ForEach-Object { "$($_.Action):$($_.FeatureId)" } | Sort-Object)
+
+        foreach ($language in @('nl-NL', 'pt-BR', 'en-US')) {
+            $script:Lang = Import-LanguageFile -LanguageCode $language
+            Update-MainWindowTweakLanguage -Window $window
+            [object]::ReferenceEquals($window.FindName('Feature_DisableTelemetry_Combo'), $checkbox) | Should -BeTrue
+            $checkbox.Content | Should -Be (Get-Translation -Key 'DisableTelemetry' -Field 'Label' -Section 'Features')
+            $checkbox.ToolTip.Text | Should -Be (Get-Translation -Key 'DisableTelemetry' -Field 'ToolTip' -Section 'Features')
+            $disabled.IsEnabled | Should -BeFalse
+            $disabled.DisableWhenApplied | Should -BeTrue
+            $disabled.ToolTip.Text | Should -Be (Get-Translation -Key 'TweaksAlreadyAppliedTooltip')
+            [object]::ReferenceEquals($group.SelectedItem, $selectedItem) | Should -BeTrue
+            $group.SelectedIndex | Should -Be 2
+            $selectedItem.Content | Should -Be (Get-GroupValueTranslation -GroupId 'SearchIcon' -FeatureId $script:UiControlMappings['Group_SearchIconCombo'].Values[1].FeatureIds[0] -FallbackLabel 'fallback')
+            @(Get-PendingTweakActions -Window $window -ShowAppliedTweaksMode $true | ForEach-Object { "$($_.Action):$($_.FeatureId)" } | Sort-Object) | Should -Be $before
+            $script:FeatureLabelLookup['DisableTelemetry'] | Should -Be $checkbox.Content
+            foreach ($category in $script:CategoryLanguageControls) {
+                $category.Header.Text | Should -Be (Get-Translation -Key $category.CategoryId -Field 'Label' -Section 'Categories')
+            }
+        }
+        $script:SelectionChanges | Should -Be 0
+    }
+
+    It 'updates app display and search metadata while preserving removal IDs and selection' {
+        $panel = [System.Windows.Controls.StackPanel]::new()
+        $app = [System.Windows.Controls.CheckBox]::new()
+        $app.IsChecked = $true
+        $app.Tag = 'Microsoft.WindowsCalculator, Other.Id'
+        $app | Add-Member -NotePropertyMembers @{
+            AppIds = @('Microsoft.WindowsCalculator', 'Other.Id'); AppName = ''; AppDescription = ''
+            AppNameText = [System.Windows.Controls.TextBlock]::new()
+            AppDescriptionText = [System.Windows.Controls.TextBlock]::new()
+        }
+        [void]$panel.Children.Add($app)
+        $script:JsonPresetCheckboxes = @()
+        $script:PreloadedAppData = @('old catalog')
+
+        foreach ($language in @('nl-NL', 'pt-BR', 'en-US')) {
+            $script:Lang = Import-LanguageFile -LanguageCode $language
+            Update-MainWindowAppLanguage -AppsPanel $panel
+            $app.AppNameText.Text | Should -Be (Get-Translation -Key 'Microsoft.WindowsCalculator' -Field 'FriendlyName' -Section 'Apps')
+            $app.AppName | Should -Be $app.AppNameText.Text
+            $app.AppDescriptionText.ToolTip | Should -Be $app.AppDescription
+            $app.AppIds | Should -Be @('Microsoft.WindowsCalculator', 'Other.Id')
+            $app.Tag | Should -Be 'Microsoft.WindowsCalculator, Other.Id'
+            $app.IsChecked | Should -BeTrue
+        }
+        $script:PreloadedAppData | Should -BeNullOrEmpty
+    }
+
+    It 'refreshes search and deployment text without changing user input or selections' {
+        Mock Get-UserName { 'TestUser' }
+        Mock Update-AppsPanelSort {}
+        Mock Hide-Bubble {}
+        $window = New-LanguageTestWindow
+        New-DynamicTweakControls -Window $window -WinVersion 26100
+        $appsPanel = [System.Windows.Controls.StackPanel]::new()
+        $window.RegisterName('AppSelectionPanel', $appsPanel)
+        [void]$window.Content.Children.Add($appsPanel)
+        $app = [System.Windows.Controls.CheckBox]::new()
+        $app.IsChecked = $true
+        $app.Tag = 'Microsoft.WindowsCalculator'
+        $app | Add-Member -NotePropertyMembers @{
+            AppIds = @('Microsoft.WindowsCalculator'); AppName = 'Calculator'; AppDescription = ''
+            AppNameText = [System.Windows.Controls.TextBlock]::new()
+            AppDescriptionText = [System.Windows.Controls.TextBlock]::new()
+        }
+        [void]$appsPanel.Children.Add($app)
+        foreach ($name in @('UserSelectionDescription', 'UsernameValidationMessage', 'AppSelectionStatus', 'AppRemovalScopeDescription', 'AppSearchPlaceholder', 'TweakSearchPlaceholder')) {
+            $window.RegisterName($name, [System.Windows.Controls.TextBlock]::new())
+        }
+        foreach ($name in @('OtherUsernameTextBox', 'AppSearchBox', 'TweakSearchBox')) {
+            $window.RegisterName($name, [System.Windows.Controls.TextBox]::new())
+        }
+        $userCombo = [System.Windows.Controls.ComboBox]::new()
+        foreach ($label in @('Current', 'Other', 'Default')) {
+            [void]$userCombo.Items.Add([System.Windows.Controls.ComboBoxItem]::new())
+        }
+        $userCombo.SelectedIndex = 1
+        $window.RegisterName('UserSelectionCombo', $userCombo)
+        $window.FindName('OtherUsernameTextBox').Text = 'Alice'
+        $scope = [System.Windows.Controls.ComboBox]::new()
+        $target = [System.Windows.Controls.ComboBoxItem]::new()
+        $target.Name = 'AppRemovalScopeTargetUser'
+        [void]$scope.Items.Add($target)
+        $scope.SelectedIndex = 0
+        $window.RegisterName('AppRemovalScopeCombo', $scope)
+        $window.RegisterName('AppRemovalScopeSection', [System.Windows.Controls.Border]::new())
+        $tabs = [System.Windows.Controls.TabControl]::new()
+        foreach ($label in @('Home', 'Apps', 'Tweaks', 'Deploy')) { [void]$tabs.Items.Add($label) }
+        $tabs.SelectedIndex = 2
+        $window.RegisterName('MainTabControl', $tabs)
+        $appSearchBox = $window.FindName('AppSearchBox')
+        $appSearchPlaceholder = $window.FindName('AppSearchPlaceholder')
+        $tweakSearchBox = $window.FindName('TweakSearchBox')
+        $tweakSearchPlaceholder = $window.FindName('TweakSearchPlaceholder')
+        $tweaksScrollViewer = $null
+        $appSearchBox.Text = 'rekenmachine'
+        $tweakSearchBox.Text = 'telemetrie'
+        $appSearchBox.Add_TextChanged($script:SearchHandlers['appSearchBox'])
+        $tweakSearchBox.Add_TextChanged($script:SearchHandlers['tweakSearchBox'])
+        $script:AppSearchMatches = @(); $script:AppSearchMatchIndex = -1
+        $script:JsonPresetCheckboxes = @()
+        $script:SortColumn = 'Name'; $script:SortAscending = $true
+        $window.Resources['SearchHighlightColor'] = [System.Windows.Media.Brushes]::Yellow
+        $window.Resources['SearchHighlightActiveColor'] = [System.Windows.Media.Brushes]::Orange
+        $checkbox = $window.FindName('Feature_DisableTelemetry_Combo')
+        $checkbox.IsChecked = $true
+
+        $script:Lang = Import-LanguageFile -LanguageCode 'nl-NL'
+        Update-MainWindowLanguage -Window $window
+
+        $userCombo.SelectedIndex | Should -Be 1
+        $scope.SelectedItem | Should -Be $target
+        $window.FindName('OtherUsernameTextBox').Text | Should -Be 'Alice'
+        $tabs.SelectedIndex | Should -Be 2
+        $appSearchBox.Text | Should -Be 'rekenmachine'
+        $tweakSearchBox.Text | Should -Be 'telemetrie'
+        $script:AppSearchMatches.Count | Should -Be 1
+        [object]::ReferenceEquals($script:AppSearchMatches[0], $app) | Should -BeTrue
+        $checkbox.Background | Should -Be ([System.Windows.Media.Brushes]::Yellow)
+        $checkbox.IsChecked | Should -BeTrue
+        $app.IsChecked | Should -BeTrue
+        $window.FindName('AppSelectionStatus').Text | Should -Be (Get-Translation -Key 'AppSelectionStatusSelected' -Count 1 -FormatArgs @(1))
+        $window.FindName('UserSelectionDescription').Text | Should -Be (Get-Translation -Key 'DeployUserDescriptionOtherUserNamed' -FormatArgs @('Alice'))
+        $window.FindName('AppRemovalScopeDescription').Text | Should -Be (Get-Translation -Key 'AppRemovalScopeDescriptionTargetUser')
+        $script:UpdatingLanguage | Should -BeFalse
+    }
+}
+
+Describe 'Settings update the same window after Save' {
+    BeforeEach {
+        $script:IsLoadingApps = $false
+        $script:UiPreferences = @{ Theme = 'Auto'; Language = 'en-US' }
+        $script:Lang = [PSCustomObject]@{ LanguageCode = 'en-US' }
+        Mock Set-WindowThemeResources {}
+        Mock Update-MainWindowLanguage {}
+        $script:WindowClosed = $false
+        $script:WindowUnderTest = New-LanguageTestWindow
+        $script:WindowUnderTest.Add_Closed({ $script:WindowClosed = $true })
+    }
+
+    It 'updates a saved theme without changing language or closing the window' {
+        Mock Show-SettingsDialog { $script:UiPreferences.Theme = 'Dark'; return $true }
+        Open-MainWindowSettings -Window $script:WindowUnderTest
+        Should -Invoke Set-WindowThemeResources -Times 1 -Exactly -ParameterFilter { $usesDarkMode -eq $true }
+        Should -Invoke Update-MainWindowLanguage -Times 0 -Exactly
+        $script:WindowClosed | Should -BeFalse
+    }
+
+    It 'updates a saved language without closing the window' {
+        Mock Show-SettingsDialog {
+            $script:Lang = [PSCustomObject]@{ LanguageCode = 'nl-NL' }
+            $script:UiPreferences.Theme = 'Dark'
+            return $true
+        }
+        Open-MainWindowSettings -Window $script:WindowUnderTest
+        Should -Invoke Update-MainWindowLanguage -Times 1 -Exactly -ParameterFilter { [object]::ReferenceEquals($Window, $script:WindowUnderTest) }
+        Should -Invoke Set-WindowThemeResources -Times 1 -Exactly -ParameterFilter { $usesDarkMode -eq $true }
+        $script:WindowClosed | Should -BeFalse
+    }
+
+    It 'does not update presentation when the settings dialog is cancelled' {
+        Mock Show-SettingsDialog { $false }
+        Open-MainWindowSettings -Window $script:WindowUnderTest
+        Should -Invoke Set-WindowThemeResources -Times 0 -Exactly
+        Should -Invoke Update-MainWindowLanguage -Times 0 -Exactly
+        $script:WindowClosed | Should -BeFalse
+    }
+}
diff --git a/Tests/Ui-Preferences.Tests.ps1 b/Tests/Ui-Preferences.Tests.ps1
new file mode 100644
index 0000000..dae93d4
--- /dev/null
+++ b/Tests/Ui-Preferences.Tests.ps1
@@ -0,0 +1,86 @@
+BeforeAll {
+    $script:RepoRoot = Split-Path $PSScriptRoot -Parent
+    . "$script:RepoRoot/Scripts/GUI/Ui-Preferences.ps1"
+    . "$script:RepoRoot/Scripts/GUI/Get-SystemUsesDarkMode.ps1"
+    . "$script:RepoRoot/Scripts/FileIO/Import-JsonFile.ps1"
+    . "$script:RepoRoot/Scripts/FileIO/Import-LanguageFile.ps1"
+    $script:LanguagesPath = Join-Path $script:RepoRoot 'Config/Languages'
+}
+
+Describe 'UI preference initialization' {
+    BeforeEach {
+        $script:UiPreferencesFilePath = "$TestDrive/preferences.json"
+        Save-UiPreferences -Preferences @{ Theme = 'Dark'; Language = 'nl-NL' }
+    }
+
+    It 'loads the saved language and theme' {
+        Initialize-UiPreferences
+        $script:UiPreferences.Theme | Should -Be 'Dark'
+        $script:UiPreferences.Language | Should -Be 'nl-NL'
+        $script:Lang.LanguageCode | Should -Be 'nl-NL'
+    }
+
+    It 'honors an explicit language without persisting the override' {
+        Initialize-UiPreferences -Language 'pt-BR'
+        $script:UiPreferences.Language | Should -Be 'pt-BR'
+        $script:Lang.LanguageCode | Should -Be 'pt-BR'
+        (Get-UiPreferences).Language | Should -Be 'nl-NL'
+    }
+
+    It 'keeps Auto as a preference while resolving the system language' {
+        Initialize-UiPreferences -Language 'Auto'
+        $script:UiPreferences.Language | Should -Be 'Auto'
+        $script:Lang.LanguageCode | Should -Be (Import-LanguageFile).LanguageCode
+    }
+
+    It 'normalizes <Language> to the resolved folder' -ForEach @(
+        @{ Language = 'nl-BE'; Expected = 'nl-NL' }
+        @{ Language = 'fr-FR'; Expected = 'en-US' }
+    ) {
+        Initialize-UiPreferences -Language $Language
+        $script:UiPreferences.Language | Should -Be $Expected
+        $script:Lang.LanguageCode | Should -Be $Expected
+    }
+
+    It 'leaves language failure handling to the caller' {
+        Mock Get-UiLanguage { $null }
+        Initialize-UiPreferences
+        $script:Lang | Should -BeNullOrEmpty
+    }
+}
+
+Describe 'UI preference persistence and theme resolution' {
+    It 'defaults to system settings when no preferences exist' {
+        $result = Get-UiPreferences -Path "$TestDrive/missing.json"
+        $result.Theme | Should -Be 'Auto'
+        $result.Language | Should -Be 'Auto'
+    }
+    It 'round trips explicit preferences' {
+        Save-UiPreferences -Preferences @{Theme='Dark'; Language='pt-BR'} -Path "$TestDrive/preferences.json"
+        $result = Get-UiPreferences -Path "$TestDrive/preferences.json"
+        $result.Theme | Should -Be 'Dark'
+        $result.Language | Should -Be 'pt-BR'
+    }
+    It 'ignores unsupported preferences' {
+        '{"Theme":"Unknown","Language":"../other"}' | Set-Content "$TestDrive/invalid.json"
+        $result = Get-UiPreferences -Path "$TestDrive/invalid.json"
+        $result.Theme | Should -Be 'Auto'
+        $result.Language | Should -Be 'Auto'
+    }
+    It 'keeps the previous settings when writing fails' {
+        Save-UiPreferences -Preferences @{Theme='Light'; Language='en-US'} -Path "$TestDrive/safe.json"
+        Mock Set-Content { throw 'Disk full' }
+        { Save-UiPreferences -Preferences @{Theme='Dark'; Language='pt-BR'} -Path "$TestDrive/safe.json" } | Should -Throw
+        (Get-UiPreferences -Path "$TestDrive/safe.json").Theme | Should -Be 'Light'
+    }
+    It 'honors explicit themes and resolves Auto from Windows' {
+        Mock Get-SystemUsesDarkMode { $true }
+        $script:UiPreferences = @{Theme='Light'}
+        Get-AppUsesDarkMode | Should -BeFalse
+        $script:UiPreferences.Theme = 'Dark'
+        Get-AppUsesDarkMode | Should -BeTrue
+        $script:UiPreferences.Theme = 'Auto'
+        Get-AppUsesDarkMode | Should -BeTrue
+        Should -Invoke Get-SystemUsesDarkMode -Times 1 -Exactly
+    }
+}
diff --git a/Win11Debloat.ps1 b/Win11Debloat.ps1
index d3a01ad..572cb0e 100644
--- a/Win11Debloat.ps1
+++ b/Win11Debloat.ps1
@@ -184,6 +184,7 @@ $script:AppsListFilePath = Join-Path $configPath 'Apps.json'
 $script:DefaultSettingsFilePath = Join-Path $configPath 'DefaultSettings.json'
 $script:FeaturesFilePath = Join-Path $configPath 'Features.json'
 $script:SavedSettingsFilePath = Join-Path $configPath 'LastUsedSettings.json'
+$script:UiPreferencesFilePath = Join-Path $env:LOCALAPPDATA 'Win11Debloat\Preferences.json'
 $script:LanguagesPath = Join-Path $configPath 'Languages'
 $script:DefaultLanguagePath = Join-Path $script:LanguagesPath 'en-US'
 $script:DefaultLogPath = Join-Path $logsPath 'Win11Debloat.log'
@@ -405,6 +406,9 @@ if (-not $script:WingetInstalled -and -not $Silent) {
 
 # GUI functions
 . "$PSScriptRoot/Scripts/GUI/Get-SystemUsesDarkMode.ps1"
+. "$PSScriptRoot/Scripts/GUI/Ui-Preferences.ps1"
+. "$PSScriptRoot/Scripts/GUI/MainWindow-Localization.ps1"
+. "$PSScriptRoot/Scripts/GUI/Show-SettingsDialog.ps1"
 . "$PSScriptRoot/Scripts/GUI/Set-WindowThemeResources.ps1"
 . "$PSScriptRoot/Scripts/GUI/Attach-ShiftClickBehavior.ps1"
 . "$PSScriptRoot/Scripts/GUI/Apply-SettingsToUiControls.ps1"
@@ -465,9 +469,8 @@ $WinVersion = Get-ItemPropertyValue 'HKLM:\SOFTWARE\Microsoft\Windows NT\Current
 # Check if the machine supports Modern Standby, this is used to determine if the DisableModernStandbyNetworking option can be used
 $script:ModernStandbySupported = Test-ModernStandbySupport
 
-# Load the GUI's language content. -Language overrides the current user's system UI culture,
-# falling back to en-US either way if the requested language isn't available.
-$script:Lang = if ($Language) { Import-LanguageFile -LanguageCode $Language } else { Import-LanguageFile }
+# Explicit -Language takes precedence over saved UI preferences and the system culture.
+Initialize-UiPreferences -Language $Language
 
 $script:Params = $PSBoundParameters
 $script:UndoParams = @{}