[auth] Support both Chinese Simplified and Traditional

auth/lib/locale.dart

@@ -32,6 +32,7 @@ const List<Locale> appSupportedLocales = <Locale>[
   Locale('uk'),
   Locale('vi'),
   Locale("zh", "CN"),
+  Locale("zh", "TW"),
 ];
 
 Locale? autoDetectedLocale;

auth/lib/ui/settings/language_picker.dart

@@ -181,6 +181,13 @@ class _ItemsWidgetState extends State<ItemsWidget> {
       case 'fi':
         return 'Suomi';
       case 'zh':
+        if (locale.countryCode == 'TW') {
+          return '中文 (台灣)';
+        } else if (locale.countryCode == 'HK') {
+          return '中文 (香港)';
+        } else if (locale.countryCode == 'CN') {
+          return '中文 (中国)';
+        }
         switch (locale.scriptCode) {
           case 'Hans':
             return '中文 (简体)';