Make the supported-language list a single source of truth so community
translations show up with no code change: add res/xml/locales_config.xml
(en, de) and reference it via android:localeConfig, which also surfaces the
per-app language entry in Android 13+ system settings.
Rewrite AppLanguage to parse locales_config.xml for the supported BCP-47
tags and expose currentTag/apply/displayName (autonyms), dropping the
hardcoded LanguagePref enum; the Settings picker is now built from that list.
Remove the now-unused settings_language_german/english strings.
Adding a language is now: drop in values-<tag>/strings.xml and add one
<locale> line.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
