Check translation contracts offline, add Swedish to the installer and enable the website languages

- Offline checks for terminal and website catalogs reject translations that change commands, paths, identifiers or placeholders
- Terminal and documentation texts that broke those contracts are corrected in every language
- Swedish can be chosen in the stable and beta installers
- The website routes, language switcher and exported pages cover the eight languages, with the shared website texts in each of them
- Website documentation translations are generated only when requested
- From PR #475 by @jcastro

web/scripts/localize-export.mjs

@@ -0,0 +1,32 @@
+// Next's shared root layout cannot read its nested [locale] parameter.
+// Set the static document language before Pagefind indexes the export, so
+// search and no-JavaScript readers see the same locale as the hydrated app.
+import { readdir, readFile, writeFile } from 'node:fs/promises'
+import { join } from 'node:path'
+
+async function htmlFiles(directory) {
+  const entries = await readdir(directory, { withFileTypes: true })
+  const files = await Promise.all(entries.map(entry => {
+    const path = join(directory, entry.name)
+    return entry.isDirectory() ? htmlFiles(path) : entry.isFile() && entry.name.endsWith('.html') ? [path] : []
+  }))
+  return files.flat()
+}
+
+let count = 0
+for (const entry of await readdir('out', { withFileTypes: true })) {
+  if (!entry.isDirectory() || !/^[a-z]{2}(?:-[a-z0-9]+)?$/.test(entry.name)) continue
+  const locale = entry.name
+  for (const file of await htmlFiles(join('out', locale))) {
+    const original = await readFile(file, 'utf8')
+    const updated = original.replace(/<html\b([^>]*)>/i, (tag, attributes) => {
+      const next = /\blang\s*=\s*["'][^"']*["']/i.test(attributes)
+        ? attributes.replace(/\blang\s*=\s*["'][^"']*["']/i, `lang="${locale}"`)
+        : `${attributes} lang="${locale}"`
+      return `<html${next}>`
+    })
+    if (updated !== original) await writeFile(file, updated, 'utf8')
+    count += 1
+  }
+}
+console.log(`Static document language verified for ${count} localized pages.`)