[auth] Enable l10n for Vietnamese, Arabic, Greek, & Slovak

auth/lib/locale.dart

@@ -5,8 +5,10 @@ import 'package:shared_preferences/shared_preferences.dart';
 // Add more language to the list only when at least 90% of the strings are
 // translated in the corresponding language.
 const List<Locale> appSupportedLocales = <Locale>[
+  Locale('ar'),
   Locale('bg'),
   Locale('de'),
+  Locale('el'),
   Locale('en'),
   Locale('es', 'ES'),
   Locale('fa'),
@@ -17,8 +19,10 @@ const List<Locale> appSupportedLocales = <Locale>[
   Locale('pl'),
   Locale('pt', 'BR'),
   Locale('ru'),
+  Locale('sk'),
   Locale('tr'),
   Locale('uk'),
+  Locale('vi'),
   Locale("zh", "CN"),
 ];
 

auth/lib/ui/settings/language_picker.dart

@@ -124,10 +124,14 @@ class _ItemsWidgetState extends State<ItemsWidget> {
 
   String _getLanguageName(Locale locale) {
     switch (locale.languageCode) {
+      case 'ar':
+        return 'العربية';
       case 'en':
         return 'English';
       case 'bg':
         return 'Български';
+      case 'el':
+        return 'Ελληνικά';
       case 'es':
         switch (locale.countryCode) {
           case 'ES':
@@ -154,10 +158,14 @@ class _ItemsWidgetState extends State<ItemsWidget> {
         }
       case 'ru':
         return 'Русский';
+      case 'sk':
+        return 'Slovenčina';
       case 'tr':
         return 'Türkçe';
       case 'uk':
         return 'Українська';
+      case 'vi':
+        return 'Tiếng Việt';
       case 'fi':
         return 'Suomi';
       case 'zh':