fix: include Japanese

ui/flutter/lib/util/locale_manager.dart

@@ -0,0 +1,13 @@
+import 'package:flutter/material.dart';
+
+Locale toLocale(String key) {
+  final arr = key.split('_');
+  return Locale(arr[0], arr[1]);
+}
+
+String getLocaleKey(Locale locale) {
+  return '${locale.languageCode}_${locale.countryCode}';
+}
+
+const debugLocale = Locale('zh', 'CN');
+const fallbackLocale = Locale('en', 'US');