flutter: intl: Fix string tapBackAgainToLeave when locale is not en

src/ui/flutter_app/lib/l10n/resources.dart

@@ -0,0 +1,62 @@
+/*
+  This file is part of Sanmill.
+  Copyright (C) 2019-2021 The Sanmill developers (see AUTHORS file)
+
+  Sanmill is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Sanmill is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+import 'dart:io';
+
+/// Interface strings
+abstract class Strings {
+  String get tapBackAgainToLeave;
+}
+
+/// English strings
+class EnglishStrings extends Strings {
+  @override
+  String get tapBackAgainToLeave => 'Tap back again to leave.';
+}
+
+/// German strings
+class GermanStrings extends Strings {
+  @override
+  String get tapBackAgainToLeave => 'Nochmal drücken um zu Beenden.';
+}
+
+/// Chinese strings
+class ChineseStrings extends Strings {
+  @override
+  String get tapBackAgainToLeave => '再次按返回键退出应用';
+}
+
+class Resources {
+  Resources();
+
+  Strings get strings {
+    String deviceLanguage = Platform.localeName.substring(0, 2);
+    switch (deviceLanguage) {
+      case 'de':
+        return GermanStrings();
+      case 'zh':
+        return ChineseStrings();
+      default:
+        return EnglishStrings();
+    }
+  }
+
+  static Resources of() {
+    return Resources();
+  }
+}

src/ui/flutter_app/lib/main.dart

@@ -26,6 +26,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_localizations/flutter_localizations.dart';
 import 'package:path_provider/path_provider.dart';
 import 'package:sanmill/generated/l10n.dart';
+import 'package:sanmill/l10n/resources.dart';
 import 'package:sanmill/services/audios.dart';
 import 'package:sanmill/style/app_theme.dart';
 import 'package:sanmill/widgets/navigation_home_screen.dart';
@@ -146,8 +147,8 @@ class _SanmillAppState extends State<SanmillApp> {
       home: Scaffold(
         body: DoubleBackToCloseApp(
           child: NavigationHomeScreen(),
-          snackBar: const SnackBar(
-            content: Text('Tap back again to leave.'),
+          snackBar: SnackBar(
+            content: Text(Resources.of().strings.tapBackAgainToLeave),
           ),
         ),
       ),