效果图如下

效果图

为什么要设置国际化

• 系统组件默认为英文
• 各个平台统一标准
• TextField、 AlertDialog、 DatePicker
• 中英文转换：localization

1.添加依赖库

需要用到flutter_localizations包，在pubspec.yaml文件中添加如下依赖

dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter

2.代码抽取封装

• 实现LocalizationsDelegate代理

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter/cupertino.dart';
import 'package:fpdxapp/utils/localization/more.dart';

class HKLocalizationDelegate extends LocalizationsDelegate<CupertinoLocalizations> {

  HKLocalizationDelegate();

  ///是否支持某个Local
  ///支持中文和英语
  @override
  bool isSupported(Locale locale) {
    return ['zh', 'en'].contains(locale.languageCode);
  }

  ///shouldReload的返回值决定当Localizations Widget重新build时，是否调用load方法重新加载Locale资源
  @override
  bool shouldReload(LocalizationsDelegate<CupertinoLocalizations> old) {
    return false;
  }

  ///根据locale，创建一个对象用于提供当前locale下的文本显示
  ///Flutter会调用此类加载相应的Locale资源类
  @override
  Future<CupertinoLocalizations> load(Locale locale) {
    return SynchronousFuture<CupertinoLocalizations>(
        MoreLocalization(locale)
    );
  }

  static HKLocalizationDelegate delegate = HKLocalizationDelegate();
}

• 通过 MoreLocalization implements CupertinoLocalizations 设置currentLocalized

import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';

class MoreLocalization implements CupertinoLocalizations{

  final Locale locale;

  MoreLocalization(this.locale);

  /// 基于Map，根据当前语言的 languageCode： en或zh来获取对应的文案
  static Map<String, BaseLanguage> _localValue = {
    'en' : EnLanguage(),
    'zh' : ChLanguage()
  };

  /// 返回当前的内容维护类
  BaseLanguage get currentLocalized {
    return _localValue[locale.languageCode];
  }

  ///通过 Localizations.of(context,type) 加载当前的 FZLocalizations
  static MoreLocalization of(BuildContext context) {
    return CupertinoLocalizations.of(context);
    /// 实现CupertinoLocalizations抽象类后，取不到对象，得换成CupertinoLocalizations.of(context);
//    return Localizations.of(context, MoreLocalization);
  }

  @override
  String get selectAllButtonLabel {
    return currentLocalized.selectAllButtonLabel;
  }

  @override
  String get pasteButtonLabel {
    return currentLocalized.pasteButtonLabel;
  }

  @override
  String get copyButtonLabel {
    return currentLocalized.copyButtonLabel;
  }

  @override
  String get cutButtonLabel {
    return currentLocalized.cutButtonLabel;
  }

  @override
  String get todayLabel {
    return "今天";
  }

  static const List<String> _shortWeekdays = <String>[
    '周一',
    '周二',
    '周三',
    '周四',
    '周五',
    '周六',
    '周日',
  ];

  static const List<String> _shortMonths = <String>[
    'Jan',
    'Feb',
    'Mar',
    'Apr',
    'May',
    'Jun',
    'Jul',
    'Aug',
    'Sep',
    'Oct',
    'Nov',
    'Dec',
  ];

  static const List<String> _months = <String>[
    '01月',
    '02月',
    '03月',
    '04月',
    '05月',
    '06月',
    '07月',
    '08月',
    '09月',
    '10月',
    '11月',
    '12月',
  ];

  @override
  String datePickerYear(int yearIndex) => yearIndex.toString() + "年";

  @override
  String datePickerMonth(int monthIndex) => _months[monthIndex - 1];

  @override
  String datePickerDayOfMonth(int dayIndex) => dayIndex.toString() + "日";

  @override
  String datePickerHour(int hour) => hour.toString();

  @override
  String datePickerHourSemanticsLabel(int hour) => hour.toString() + " 小时";

  @override
  String datePickerMinute(int minute) => minute.toString().padLeft(2, '0');

  @override
  String datePickerMinuteSemanticsLabel(int minute) {
    return '1 分钟';
  }

  @override
  String datePickerMediumDate(DateTime date) {
    return '${_shortWeekdays[date.weekday - DateTime.monday]} '
        '${_shortMonths[date.month - DateTime.january]} '
        '${date.day.toString().padRight(2)}';
  }

  @override
  DatePickerDateOrder get datePickerDateOrder => DatePickerDateOrder.ymd;

  @override
  DatePickerDateTimeOrder get datePickerDateTimeOrder => DatePickerDateTimeOrder.date_time_dayPeriod;

  @override
  String get anteMeridiemAbbreviation => 'AM';

  @override
  String get postMeridiemAbbreviation => 'PM';

  @override
  String get alertDialogLabel => '提示信息';

  @override
  String timerPickerHour(int hour) => hour.toString();

  @override
  String timerPickerMinute(int minute) => minute.toString();

  @override
  String timerPickerSecond(int second) => second.toString();

  @override
  String timerPickerHourLabel(int hour) => '时';

  @override
  String timerPickerMinuteLabel(int minute) => '分';

  @override
  String timerPickerSecondLabel(int second) => '秒';

}

/// 这个抽象类和它的实现类可以拉出去新建类
/// 中文和英语 语言内容维护
abstract class BaseLanguage {
  String name;
  String selectAllButtonLabel;
  String pasteButtonLabel;
  String copyButtonLabel;
  String cutButtonLabel;
}

class EnLanguage implements BaseLanguage {

  @override
  String name = "This is English";
  @override
  String selectAllButtonLabel = "全选 英语";
  @override
  String pasteButtonLabel = "PASTE";
  @override
  String copyButtonLabel = "COPY";
  @override
  String cutButtonLabel = "CUT";
}

class ChLanguage implements BaseLanguage {

  @override
  String name = "这是中文";
  @override
  String selectAllButtonLabel = "全选";
  @override
  String pasteButtonLabel = "粘贴";
  @override
  String copyButtonLabel = "复制";
  @override
  String cutButtonLabel = "剪切";

}

• 如何使用
  • 导入依赖库 import 'package:flutter_localizations/flutter_localizations.dart';
  • 在Material中设置localizationsDelegates、supportedLocales和localeListResolutionCallback

MaterialApp(
    title: 'App',
    localizationsDelegates: [
      /// 本地化的代理类
      GlobalMaterialLocalizations.delegate,
      GlobalWidgetsLocalizations.delegate,
      /// 注册我们的Delegate
      HKLocalizationDelegate.delegate
    ],
    supportedLocales: [
      const Locale('en', 'US'), // 美国英语
      const Locale('zh', 'CN'), // 中文简体
    ],
    /// 监听系统语言切换
    localeListResolutionCallback: (deviceLocale, supportedLocales){
      print('deviceLocale: $deviceLocale');
      // 系统语言是英语： deviceLocale: [en_CN, en_CN, zh_Hans_CN]
      // 系统语言是中文： deviceLocale: [zh_CN, zh_Hans_CN, en_CN]
      print('supportedLocales: $supportedLocales');
    },

  )

TextField光标不对齐

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      localizationsDelegates: [
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      supportedLocales: [const Locale('zh', 'CH'), const Locale('en', 'US')],
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        padding: EdgeInsets.all(32),
        child: Center(
          child: TextField(
            decoration: InputDecoration(hintText: '测试提示'),
          ),
        ),
      ),
    );
  }
}

如何修复TextField光标不对齐

TextField > style > textBaseline: TextBaseline.alphabetic

官方文档：
https://api.flutter.dev/flutter/flutter_localizations/flutter_localizations-library.html