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┌─────────────────────────────────────────────┐
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│  ARB 파일 (번역 원본)                         │
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│  app_ko.arb, app_en.arb, app_ja.arb         │
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└─────────────────┬───────────────────────────┘
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                  │ flutter gen-l10n
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                  ▼
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┌─────────────────────────────────────────────┐
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│  생성된 Dart 코드                            │
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│  AppLocalizations 클래스                     │
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└─────────────────┬───────────────────────────┘
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                  │
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                  ▼
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┌─────────────────────────────────────────────┐
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│  앱에서 사용                                 │
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│  AppLocalizations.of(context)!.hello        │
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└─────────────────────────────────────────────┘

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dependencies:
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  flutter:
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    sdk: flutter
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  flutter_localizations:  # Flutter 위젯 번역
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    sdk: flutter
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  intl: any               # 날짜/숫자 형식화
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flutter:
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  generate: true          # l10n 코드 자동 생성 활성화

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arb-dir: lib/l10n
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template-arb-file: app_en.arb
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output-localization-file: app_localizations.dart

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{
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  "@@locale": "en",
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  "appTitle": "My App",
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  "@appTitle": {
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    "description": "The title of the application"
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  },
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  "hello": "Hello {name}!",
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  "@hello": {
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    "description": "Greeting message",
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    "placeholders": {
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      "name": {
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        "type": "String",
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        "example": "John"
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      }
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    }
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  },
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  "itemCount": "{count, plural, =0{No items} =1{1 item} other{{count} items}}",
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  "@itemCount": {
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    "description": "Shows number of items",
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    "placeholders": {
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      "count": {
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        "type": "int"
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      }
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    }
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  }
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}

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{
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  "@@locale": "ko",
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  "appTitle": "내 앱",
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  "hello": "안녕하세요, {name}님!",
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  "itemCount": "{count, plural, =0{항목 없음} other{{count}개 항목}}"
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}

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"greeting": "Hello, {userName}!"

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"messages": "{count, plural, =0{No messages} =1{1 message} other{{count} messages}}"

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"pronoun": "{gender, select, male{He} female{She} other{They}}"

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"lastLogin": "Last login: {date}",
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"@lastLogin": {
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  "placeholders": {
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    "date": {
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      "type": "DateTime",
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      "format": "yMd"
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    }
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  }
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}

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import 'package:flutter/material.dart';
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import 'package:flutter_localizations/flutter_localizations.dart';
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import 'package:flutter_gen/gen_l10n/app_localizations.dart';
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void main() {
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  runApp(const MyApp());
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}
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class MyApp extends StatelessWidget {
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  const MyApp({super.key});
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  @override
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  Widget build(BuildContext context) {
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    return MaterialApp(
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      title: 'My App',
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      // 지원하는 로케일 목록
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      supportedLocales: AppLocalizations.supportedLocales,
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      // 지역화 델리게이트 목록
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      localizationsDelegates: AppLocalizations.localizationsDelegates,
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      home: const HomePage(),
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    );
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  }
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}

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import 'package:flutter_gen/gen_l10n/app_localizations.dart';
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class HomePage extends StatelessWidget {
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  const HomePage({super.key});
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  @override
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  Widget build(BuildContext context) {
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    // 현재 로케일에 맞는 번역 객체 가져오기
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    final l10n = AppLocalizations.of(context)!;
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    return Scaffold(
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      appBar: AppBar(
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        title: Text(l10n.appTitle),  // "내 앱" (한국어)
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      ),
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      body: Center(
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        child: Column(
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          mainAxisAlignment: MainAxisAlignment.center,
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          children: [
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            // 변수 치환
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            Text(l10n.hello('홍길동')),  // "안녕하세요, 홍길동님!"
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            // 복수형
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            Text(l10n.itemCount(0)),   // "항목 없음"
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            Text(l10n.itemCount(1)),   // "1개 항목"
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            Text(l10n.itemCount(5)),   // "5개 항목"
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          ],
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        ),
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      ),
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    );
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  }
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}

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extension BuildContextL10n on BuildContext {
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  AppLocalizations get l10n => AppLocalizations.of(this)!;
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}
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// 사용
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class MyWidget extends StatelessWidget {
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  @override
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  Widget build(BuildContext context) {
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    return Text(context.l10n.hello('Flutter'));
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  }
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}

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class MyApp extends StatefulWidget {
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  const MyApp({super.key});
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  // 전역 키를 통한 상태 접근 (간단한 예시)
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  static void setLocale(BuildContext context, Locale locale) {
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    final state = context.findAncestorStateOfType<_MyAppState>();
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    state?.setLocale(locale);
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  }
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  @override
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  State<MyApp> createState() => _MyAppState();
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}
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class _MyAppState extends State<MyApp> {
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  Locale? _locale;
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  void setLocale(Locale locale) {
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    setState(() {
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      _locale = locale;
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    });
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  }
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  @override
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  Widget build(BuildContext context) {
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    return MaterialApp(
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      locale: _locale,  // null이면 시스템 설정 사용
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      supportedLocales: AppLocalizations.supportedLocales,
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      localizationsDelegates: AppLocalizations.localizationsDelegates,
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      home: const HomePage(),
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    );
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  }
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}

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class LanguageSelector extends StatelessWidget {
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  const LanguageSelector({super.key});
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  @override
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  Widget build(BuildContext context) {
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    return DropdownButton<Locale>(
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      value: Localizations.localeOf(context),
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      items: const [
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        DropdownMenuItem(
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          value: Locale('ko'),
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          child: Text('한국어'),
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        ),
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        DropdownMenuItem(
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          value: Locale('en'),
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          child: Text('English'),
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        ),
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        DropdownMenuItem(
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          value: Locale('ja'),
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          child: Text('日本語'),
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        ),
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      ],
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      onChanged: (locale) {
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        if (locale != null) {
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          MyApp.setLocale(context, locale);
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        }
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      },
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    );
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  }
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}

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import 'package:intl/intl.dart';
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class FormattingExample extends StatelessWidget {
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  const FormattingExample({super.key});
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  @override
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  Widget build(BuildContext context) {
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    final locale = Localizations.localeOf(context).toString();
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    final now = DateTime.now();
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    final price = 1234567.89;
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    return Column(
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      children: [
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        // 날짜 형식화
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        Text(DateFormat.yMMMMd(locale).format(now)),
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        // ko: 2024년 1월 15일
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        // en: January 15, 2024
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        // 시간 형식화
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        Text(DateFormat.jm(locale).format(now)),
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        // ko: 오후 3:30
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        // en: 3:30 PM
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        // 숫자 형식화
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        Text(NumberFormat.decimalPattern(locale).format(price)),
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        // ko: 1,234,567.89
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        // de: 1.234.567,89
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        // 통화 형식화
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        Text(NumberFormat.currency(locale: locale, symbol: '₩').format(price)),
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        // ₩1,234,568
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      ],
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    );
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  }
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}

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import 'package:intl/date_symbol_data_local.dart';
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void main() async {
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  WidgetsFlutterBinding.ensureInitialized();
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  await initializeDateFormatting();  // 모든 로케일 초기화
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  runApp(const MyApp());
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}