Support language settings

assets/l10n/app_en.arb

@@ -891,6 +891,26 @@
   "@openLinksWithInAppBrowser": {
     "description": "Label for toggling setting to open links with in-app browser"
   },
+  "languageSettingTitle": "Language",
+  "@languageSettingTitle": {
+    "description": "Title for language setting."
+  },
+  "languageEn": "English",
+  "@languageEn": {
+    "description": "Label for the English language."
+  },
+  "languagePl": "Polish",
+  "@languagePl": {
+    "description": "Label for the Polish language."
+  },
+  "languageRu": "Russian",
+  "@languageRu": {
+    "description": "Label for the Russian language."
+  },
+  "languageUk": "Ukrainian",
+  "@languageUk": {
+    "description": "Label for the Ukrainian language."
+  },
   "pollWidgetQuestionMissing": "No question.",
   "@pollWidgetQuestionMissing": {
     "description": "Text to display for a poll when the question is missing"

docs/translation.md

@@ -25,6 +25,8 @@ is working correctly.
 
 ## Adding new UI strings
 
+<div id="add-string" />
+
 ### Adding a string to the translation database
 
 To add a new string in the UI, start by
@@ -79,6 +81,26 @@ For example:
 `zulipLocalizations.subscribedToNChannels(store.subscriptions.length)`.
 
 
+## Adding a new language
+
+ARB files for new languages are automatically created in pull requests generated
+by [the update-translations GitHub workflow](/.github/workflows/update-translations.yml).
+However, this won't make them in the in-app settings UI.
+
+On [Weblate](https://hosted.weblate.org/projects/zulip/zulip-flutter/),
+we can check the percentage of strings translated in each language.
+We use this information to determine if we should start offerring the language
+in the in-app settings UI.  For reference, on the web app, we offer a language
+when it is 5% translated. (Search for `percent_translated` in the server code.)
+
+When a language has a good percentage of strings translated, follow these steps
+to add it:
+
+- If the language tag is, for example, 'en-GB', [add a string](#add-string)
+  named 'languageEnGb'.
+- Update [localizations.dart](/lib/model/localizations.dart) to include the new language in
+  `languages`, following the instructions there.
+
 ## Hack to enforce locale (for testing, etc.)
 
 For testing the app's behavior in different locales,

lib/generated/l10n/zulip_localizations.dart

@@ -1313,6 +1313,36 @@ abstract class ZulipLocalizations {
   /// **'Open links with in-app browser'**
   String get openLinksWithInAppBrowser;
 
+  /// Title for language setting.
+  ///
+  /// In en, this message translates to:
+  /// **'Language'**
+  String get languageSettingTitle;
+
+  /// Label for the English language.
+  ///
+  /// In en, this message translates to:
+  /// **'English'**
+  String get languageEn;
+
+  /// Label for the Polish language.
+  ///
+  /// In en, this message translates to:
+  /// **'Polish'**
+  String get languagePl;
+
+  /// Label for the Russian language.
+  ///
+  /// In en, this message translates to:
+  /// **'Russian'**
+  String get languageRu;
+
+  /// Label for the Ukrainian language.
+  ///
+  /// In en, this message translates to:
+  /// **'Ukrainian'**
+  String get languageUk;
+
   /// Text to display for a poll when the question is missing
   ///
   /// In en, this message translates to:

lib/generated/l10n/zulip_localizations_ar.dart

@@ -724,6 +724,21 @@ class ZulipLocalizationsAr extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'No question.';
 

lib/generated/l10n/zulip_localizations_de.dart

@@ -724,6 +724,21 @@ class ZulipLocalizationsDe extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'No question.';
 

lib/generated/l10n/zulip_localizations_en.dart

@@ -724,6 +724,21 @@ class ZulipLocalizationsEn extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'No question.';
 

lib/generated/l10n/zulip_localizations_ja.dart

@@ -724,6 +724,21 @@ class ZulipLocalizationsJa extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'No question.';
 

lib/generated/l10n/zulip_localizations_nb.dart

@@ -724,6 +724,21 @@ class ZulipLocalizationsNb extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'No question.';
 

lib/generated/l10n/zulip_localizations_pl.dart

@@ -733,6 +733,21 @@ class ZulipLocalizationsPl extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Otwieraj odnośniki w aplikacji';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'Brak pytania.';
 

lib/generated/l10n/zulip_localizations_ru.dart

@@ -737,6 +737,21 @@ class ZulipLocalizationsRu extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Открывать ссылки внутри приложения';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'Нет вопроса.';
 

lib/generated/l10n/zulip_localizations_sk.dart

@@ -726,6 +726,21 @@ class ZulipLocalizationsSk extends ZulipLocalizations {
   @override
   String get openLinksWithInAppBrowser => 'Open links with in-app browser';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'Bez otázky.';
 

lib/generated/l10n/zulip_localizations_uk.dart

@@ -737,6 +737,21 @@ class ZulipLocalizationsUk extends ZulipLocalizations {
   String get openLinksWithInAppBrowser =>
       'Відкривати посилання за допомогою браузера додатку';
 
+  @override
+  String get languageSettingTitle => 'Language';
+
+  @override
+  String get languageEn => 'English';
+
+  @override
+  String get languagePl => 'Polish';
+
+  @override
+  String get languageRu => 'Russian';
+
+  @override
+  String get languageUk => 'Ukrainian';
+
   @override
   String get pollWidgetQuestionMissing => 'Немає питання.';
 

lib/model/database.dart

@@ -1,3 +1,5 @@
+import 'dart:ui';
+
 import 'package:drift/drift.dart';
 import 'package:drift/internal/versioned_schema.dart';
 import 'package:drift/remote.dart';
@@ -24,6 +26,8 @@ class GlobalSettings extends Table {
   Column<String> get browserPreference => textEnum<BrowserPreference>()
     .nullable()();
 
+  Column<String> get language => text().map(const LocaleConverter()).nullable()();
+
   // If adding a new column to this table, consider whether [BoolGlobalSettings]
   // can do the job instead (by adding a value to the [BoolGlobalSetting] enum).
   // That way is more convenient, when it works, because
@@ -119,7 +123,7 @@ class AppDatabase extends _$AppDatabase {
   //    information on using the build_runner.
   //  * Write a migration in `_migrationSteps` below.
   //  * Write tests.
-  static const int latestSchemaVersion = 6; // See note.
+  static const int latestSchemaVersion = 7; // See note.
 
   @override
   int get schemaVersion => latestSchemaVersion;
@@ -174,6 +178,9 @@ class AppDatabase extends _$AppDatabase {
     from5To6: (m, schema) async {
       await m.createTable(schema.boolGlobalSettings);
     },
+    from6To7: (m, schema) async {
+      await m.addColumn(schema.globalSettings, schema.globalSettings.language);
+    }
   );
 
   Future<void> _createLatestSchema(Migrator m) async {
@@ -243,3 +250,55 @@ class AppDatabase extends _$AppDatabase {
 }
 
 class AccountAlreadyExistsException implements Exception {}
+
+class LocaleConverter extends TypeConverter<Locale, String> {
+  const LocaleConverter();
+
+  /// Parse a Unicode BCP 47 Language Identifier into [Locale].
+  ///
+  /// Throw when it fails to convert [languageTag] into a [Locale].
+  ///
+  /// This supports parsing a Unicode Language Identifier returned from
+  /// [Locale.toLanguageTag].
+  ///
+  /// This implementation refers to a part of
+  /// [this EBNF grammar](https://www.unicode.org/reports/tr35/#Unicode_language_identifier),
+  /// assuming the identifier is valid without
+  /// [unicode_variant_subtag](https://www.unicode.org/reports/tr35/#unicode_variant_subtag).
+  ///
+  /// This doesn't check if the [languageTag] is a valid identifier, (i.e., when
+  /// this returns without errors, the identifier is not necessarily
+  /// syntactically well-formed or valid).
+  // TODO(upstream): send this as a factory Locale.fromLanguageTag
+  //   https://github.com/flutter/flutter/issues/143491
+  Locale _fromLanguageTag(String languageTag) {
+    final subtags = languageTag.replaceAll('_', '-').split('-');
+
+    return switch (subtags) {
+      [final language, final script, final region] =>
+        Locale.fromSubtags(
+          languageCode: language, scriptCode: script, countryCode: region),
+
+      [final language, final script] when script.length == 4 =>
+        Locale.fromSubtags(languageCode: language, scriptCode: script),
+
+      [final language, final region] =>
+        Locale(language, region),
+
+      [final language] =>
+        Locale(language),
+
+      _ => throw ArgumentError.value(languageTag, 'languageTag'),
+    };
+  }
+
+  @override
+  Locale fromSql(String fromDb) {
+    return _fromLanguageTag(fromDb);
+  }
+
+  @override
+  String toSql(Locale value) {
+    return value.toLanguageTag();
+  }
+}