@bitakit/next-intl

Optional next-intl integration. Call useNextIntlPlugin() inside the configured NextIntlClientProvider and register the returned plugin with Foundation. The adapter updates the existing translation service; it does not maintain a second locale store. The host configures request locale, supported languages and message composition.

Source responsibilities

• src/index.ts: reactive translator and raw getCatalog(namespace?) integration.
• src/preferences.ts (./preferences): optional languagePreferences composition of standard App Preferences definitions, catalog section and host persistence callbacks.
• locales/en.json, locales/de.json: this integration's own language-setting labels.

languagePreferences({ locales, defaultLocale, category }) returns the setting, a normal Foundation plugin and storage(base, { load, save, reset }). Register the plugin beside App Preferences and use that storage when creating its instance. Only language.locale is routed to the supplied persistence; other preferences retain their original storage. Use a base storage with reset support to remove the locale override on reset. Configured locales become standard Select options; labels may include flags. No separate language buttons, locale state store or custom control are needed.

Content Demo persists through server actions and its validated HTTP-only locale cookie. Next updates the existing provider tree after cookie mutation. Adding a language means adding a configured option and an app catalog; missing plugin keys use the fallback catalog.

Catalog ownership and overrides

Import each installed package's ./locales/en.json and ./locales/de.json in request configuration. Compose them with the existing mergePluginMessages, then pass host catalogs as app. For the same locale and key, the app wins. Plugin text stays in its own package; the host contains only product text or deliberate overrides. Better Auth uses its published upstream locale bundles through the existing native provider.

The translation service exposes getCatalog(namespace?) alongside translate. It returns the current nested group, the full catalog without a namespace, or undefined for missing/non-object groups. Updates notify the existing subscribers.