fix: add notification language UI labels

AppImage/messages/en/common.json

@@ -1981,7 +1981,10 @@
         "systemHostname": "System hostname",
         "displayNameHint": "Name shown in notifications. Edit it or leave it empty to use the system hostname.",
         "activeFooter": "Notifications are active. Each channel follows its own category and event selection.",
-        "inactiveFooter": "Enable notifications to receive system, health and security alerts through the configured channels."
+        "inactiveFooter": "Enable notifications to receive system, health and security alerts through the configured channels.",
+        "notificationLanguage": "Notification language",
+        "selectNotificationLanguage": "Select notification language",
+        "notificationLanguageHint": "Used for deterministic runtime notifications even when AI is disabled."
       },
       "ai": {
         "title": "AI enhancement",

AppImage/messages/sk/common.json

@@ -1981,7 +1981,10 @@
         "systemHostname": "Názov systému",
         "displayNameHint": "Meno zobrazené v notifikáciách. Upravte ho alebo nechajte prázdne a použije sa názov systému.",
         "activeFooter": "Notifikácie sú aktívne. Každý kanál posiela udalosti podľa vlastného výberu kategórií.",
-        "inactiveFooter": "Zapnite notifikácie a dostávajte upozornenia o systéme, stave a bezpečnosti cez nastavené kanály."
+        "inactiveFooter": "Zapnite notifikácie a dostávajte upozornenia o systéme, stave a bezpečnosti cez nastavené kanály.",
+        "notificationLanguage": "Jazyk notifikácií",
+        "selectNotificationLanguage": "Vyberte jazyk notifikácií",
+        "notificationLanguageHint": "Používa sa pre spoľahlivé runtime notifikácie aj vtedy, keď je AI vypnutá."
       },
       "ai": {
         "title": "AI vylepšenie",

AppImage/scripts/tests/test_notification_runtime_i18n.py

@@ -70,6 +70,21 @@ class RuntimeCatalogTests(unittest.TestCase):
         for key in en:
             self.assertEqual(_placeholders(sk[key]), _placeholders(en[key]), key)
 
+    def test_notification_language_ui_keys_exist_in_both_catalogs(self):
+        required = {
+            "notificationLanguage",
+            "selectNotificationLanguage",
+            "notificationLanguageHint",
+        }
+        for language in ("en", "sk"):
+            path = APPIMAGE_DIR / "messages" / language / "common.json"
+            common = json.loads(path.read_text(encoding="utf-8"))
+            ui = common["settings"]["notifications"]["ui"]
+            self.assertTrue(required.issubset(ui), language)
+            for key in required:
+                self.assertIsInstance(ui[key], str)
+                self.assertTrue(ui[key].strip(), f"{language}:{key}")
+
     def test_slovak_catalog_preserves_placeholders_and_translates_static_text(self):
         en = self.catalogs["en"]["templates"]
         sk = self.catalogs["sk"]["templates"]