[wave-6] locale partialy implemented

assets/i18n/en.json

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+{
+  "appTitle": "Wave",
+  "@appTitle": {
+    "description": "The title of the application"
+  },
+  "start_screen": {
+    "welcome_text": "Welcome!",
+    "start_button": "Start"
+  },
+  "start_connection_screen": {
+    "create_code_text": "Create a code",
+    "initiate_text": "If you want to initiate a connection",
+    "create_button": "Create",
+    "or_text": "OR",
+    "paste_code_text": "Paste code from friend",
+    "connect_text": "If you want to connect to already created peer",
+    "paste_button": "Paste"
+  },
+  "enable_microphone_screen": {
+    "allow_access_text": "Allow access, please",
+    "mic_on_button": "Mic on"
+  },
+  "copy_code_screen": {
+    "your_code_text": "This is your two-word pair cod. Copy and send it to your friend",
+    "check_button": "Check pair",
+    "wait_text": "Wait your friend to paste the code for button enabling",
+    "fail_create_code_text": "Failed to create code"
+  },
+
+  "paste_code_screen": {
+    "paste_code_text": "Copy your friend’s code and paste it to the text input below:",
+    "connect_button": "Connect"
+  },
+
+  "connection_screen": {
+    "close_peer_button": "Close peer",
+    "warn_termination_text": "This leads to the termination of your connection",
+    "help_text": "This might help: ",
+    "return_to_prev_step_text": "Return to the previous step and try to pair once again",
+    "return_button": "Return",
+    "connected_text": "Connected",
+    "connecting_text": "Connecting",
+    "fail_to_connect_text": "Failed to connect",
+    "disconnected_text": "Disconnected",
+    "successful_connection_text": "Successful connection!",
+    "device_to_connect_text": "Waiting other device to connect..",
+    "device_to_accept_text": "Waiting your friend’s device to accept...",
+    "device_to_answer_text": "Waiting your friend’s device to answer...",
+    "failed_text": "Failed!",
+    "connection_lost_text": "Connection lost!"
+  },
+
+  "main_screen": {
+    "invalid_text": "Invalid two-word code"
+  },
+
+  "call_screen": {
+    "you_text": "You",
+    "peer_text": "Peer",
+    "encrypted_text": "Your call is end-to-end encrypted",
+    "current_input_device_text": "Current Input Device",
+    "current_output_device_text": "Current Output Device",
+    "default_microphone_text": "Default Microphone",
+    "default_speaker_text": "Default Speaker",
+    "settings_text": "Settings",
+    "leave_call_text": "Leave Call",
+    "join_call_text": "Join Call",
+    "connected_text": "Connected",
+    "call_failed_text": "Call Failed",
+    "connecting_text": "Connecting...",
+    "ready_text": "Ready to call"
+  }
+}

assets/i18n/ru.json

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+{
+  "appTitle": "Wave",
+  "@appTitle": {
+    "description": "The title of the application"
+  },
+  "start_screen": {
+    "welcome_text": "Welcome!",
+    "start_button": "Start"
+  },
+  "start_connection_screen": {
+    "create_code_text": "Create a code",
+    "initiate_text": "If you want to initiate a connection",
+    "create_button": "Create",
+    "or_text": "OR",
+    "paste_code_text": "Paste code from friend",
+    "connect_text": "If you want to connect to already created peer",
+    "paste_button": "Paste"
+  },
+  "enable_microphone_screen": {
+    "allow_access_text": "Allow access, please",
+    "mic_on_button": "Mic on"
+  },
+  "copy_code_screen": {
+    "your_code_text": "This is your two-word pair cod. Copy and send it to your friend",
+    "check_button": "Check pair",
+    "wait_text": "Wait your friend to paste the code for button enabling",
+    "fail_create_code_text": "Failed to create code"
+  },
+
+  "paste_code_screen": {
+    "paste_code_text": "Copy your friend’s code and paste it to the text input below:",
+    "connect_button": "Connect"
+  },
+
+  "connection_screen": {
+    "close_peer_button": "Close peer",
+    "warn_termination_text": "This leads to the termination of your connection",
+    "help_text": "This might help: ",
+    "return_to_prev_step_text": "Return to the previous step and try to pair once again",
+    "return_button": "Return",
+    "connected_text": "Connected",
+    "connecting_text": "Connecting",
+    "fail_to_connect_text": "Failed to connect",
+    "disconnected_text": "Disconnected",
+    "successful_connection_text": "Successful connection!",
+    "device_to_connect_text": "Waiting other device to connect..",
+    "device_to_accept_text": "Waiting your friend’s device to accept...",
+    "device_to_answer_text": "Waiting your friend’s device to answer...",
+    "failed_text": "Failed!",
+    "connection_lost_text": "Connection lost!"
+  },
+
+  "main_screen": {
+    "invalid_text": "Invalid two-word code"
+  },
+
+  "call_screen": {
+    "you_text": "You",
+    "peer_text": "Peer",
+    "encrypted_text": "Your call is end-to-end encrypted",
+    "current_input_device_text": "Current Input Device",
+    "current_output_device_text": "Current Output Device",
+    "default_microphone_text": "Default Microphone",
+    "default_speaker_text": "Default Speaker",
+    "settings_text": "Settings",
+    "leave_call_text": "Leave Call",
+    "join_call_text": "Join Call",
+    "connected_text": "Connected",
+    "call_failed_text": "Call Failed",
+    "connecting_text": "Connecting...",
+    "ready_text": "Ready to call"
+  }
+}

lib/src/i18n/localizations.dart

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+import 'dart:convert';
+import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
+
+class AppLocalisationDelegate extends LocalizationsDelegate<AppLocalizations> {
+  const AppLocalisationDelegate();
+
+  @override
+  bool isSupported(Locale locale) => AppLocalizations.isSupported(locale);
+
+  @override
+  bool shouldReload(LocalizationsDelegate<AppLocalizations> old) => false;
+
+  @override
+  Future<AppLocalizations> load(Locale locale) async {
+    final loc = AppLocalizations(AppLocalizations.fetchLocale(locale));
+    await loc.load();
+    return loc;
+  }
+}
+
+class AppLocalizations {
+  AppLocalizations(this.locale);
+  final Locale locale;
+
+  late final Map<String, String> _keys;
+
+  static const Locale defaultLocale = Locale('en');
+  static const supportedLocales = <Locale>[Locale('ru'), defaultLocale];
+  static const supportedLanguageCodes = <String>{'en', 'ru'};
+
+  static bool isSupported(Locale locale) =>
+      supportedLanguageCodes.contains(locale.languageCode);
+
+  static Locale fetchLocale(Locale locale) =>
+      isSupported(locale) ? Locale(locale.languageCode) : defaultLocale;
+
+  Future<void> load() async {
+    // 1) База en
+    final base = await _loadJsonMap('assets/i18n/en.json');
+    // 2) Текущий язык (может совпадать с en)
+    final lang = locale.languageCode;
+    final overlay = lang == 'en'
+        ? const <String, dynamic>{}
+        : await _tryLoadJsonMap('assets/i18n/$lang.json');
+
+    // merge и сплющивание в плоские ключи "a.b.c"
+    final merged = <String, dynamic>{}
+      ..addAll(base)
+      ..addAll(overlay);
+    _keys = _flatten(merged);
+  }
+
+  // ---- API ----
+
+  String t(String key, {Map<String, Object?> params = const {}}) {
+    final raw = _keys[key] ?? key;
+    if (params.isEmpty) return raw;
+    return _fillPlaceholders(raw, params);
+  }
+
+  String translate(String key, [Map<String, String>? placeholders]) =>
+      t(key, params: placeholders ?? const {});
+
+  static AppLocalizations of(BuildContext context) =>
+      Localizations.of<AppLocalizations>(context, AppLocalizations)!;
+
+  // ---- helpers ----
+
+  Future<Map<String, dynamic>> _loadJsonMap(String path) async {
+    final raw = await rootBundle.loadString(path);
+    return (json.decode(raw) as Map<String, dynamic>);
+  }
+
+  Future<Map<String, dynamic>> _tryLoadJsonMap(String path) async {
+    try {
+      final raw = await rootBundle.loadString(path);
+      return (json.decode(raw) as Map<String, dynamic>);
+    } catch (_) {
+      return const {};
+    }
+  }
+
+  Map<String, String> _flatten(Map<String, dynamic> map, {String? prefix}) {
+    final out = <String, String>{};
+
+    map.forEach((k, v) {
+      // пропускаем служебные ключи (на будущее, под ARB-стиль)
+      if (k.startsWith('@')) return;
+
+      final key = prefix == null ? k : '$prefix.$k';
+      if (v is Map) {
+        out.addAll(_flatten(v.cast<String, dynamic>(), prefix: key));
+      } else if (v is String) {
+        out[key] = v;
+      } else if (v != null) {
+        out[key] = v.toString();
+      }
+    });
+
+    return out;
+  }
+
+  String _fillPlaceholders(String text, Map<String, Object?> params) {
+    // поддерживаем как ${name}, так и {name}
+    return text.replaceAllMapped(RegExp(r'\$\{(\w+)\}|\{(\w+)\}'), (m) {
+      final key = m.group(1) ?? m.group(2)!;
+      final val = params[key];
+      return val?.toString() ?? m.group(0)!;
+    });
+  }
+}
+
+// syntactic sugar: context.l10n.t('key')
+extension L10nX on BuildContext {
+  AppLocalizations get l10n => AppLocalizations.of(this);
+}