intl: Set up basic i18n framework

Set up `flutter_localizations` integration and blank
test bundle of ARB files.

Fixes: zulip#275

assets/l10n/app_en.arb

@@ -0,0 +1 @@
+{}

assets/l10n/app_ja.arb

@@ -0,0 +1 @@
+{}

l10n.yaml

@@ -0,0 +1,11 @@
+# Docs on this config file:
+#   https://docs.flutter.dev/ui/accessibility-and-localization/internationalization#configuring-the-l10nyaml-file
+
+arb-dir: assets/l10n
+template-arb-file: app_en.arb
+required-resource-attributes: true
+output-localization-file: zulip_localizations.dart
+untranslated-messages-file: build/untranslated_messages.json
+output-class: ZulipLocalizations
+preferred-supported-locales: [ en ]
+nullable-getter: false

lib/widgets/app.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_gen/gen_l10n/zulip_localizations.dart';
 
 import '../model/narrow.dart';
 import 'about_zulip.dart';
@@ -45,6 +46,8 @@ class ZulipApp extends StatelessWidget {
     return GlobalStoreWidget(
       child: MaterialApp(
         title: 'Zulip',
+        localizationsDelegates: ZulipLocalizations.localizationsDelegates,
+        supportedLocales: ZulipLocalizations.supportedLocales,
         theme: theme,
         home: const ChooseAccountPage()));
   }

pubspec.lock

@@ -358,6 +358,11 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.0.2"
+  flutter_localizations:
+    dependency: "direct main"
+    description: flutter
+    source: sdk
+    version: "0.0.0"
   flutter_plugin_android_lifecycle:
     dependency: transitive
     description:

pubspec.yaml

@@ -57,6 +57,8 @@ dependencies:
   package_info_plus: ^4.0.1
   collection: ^1.17.2
   url_launcher: ^6.1.11
+  flutter_localizations:
+    sdk: flutter
 
 dev_dependencies:
   flutter_test:
@@ -82,6 +84,11 @@ dev_dependencies:
 # The following section is specific to Flutter packages.
 flutter:
 
+  # Generate localization bindings from ARB files in lib/l10n/.
+  # This happens automatically with `flutter run`
+  # but can be manually run with `flutter gen-l10n`
+  generate: true
+
   # The following line ensures that the Material Icons font is
   # included with your application, so that you can use the icons in
   # the material Icons class.