To configure localization add the following to the pubspec.yaml file. The file should look like below.

  # ..
    sdk: flutter
  # Localization Packages
  intl: any
  generate: true

Make sure to add the generate: true flag under flutter.

The localization files can be placed under lib/l10n folder with name app_en.arb with key value pair format for its content.

  "appTitle": "Flutter App"

Now we need to generate the localization classes from the strings defined. For that we can use the command flutter gen-l10n. But we can configure Flutter to automatically generate this file by creating an l10n.yaml file in the root directory with the following content.

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

With this we don't have to run flutter gen-l10n command each time we make changes to the arb file or in CI/CD build steps.

Now in the app initialization widget specify the localization details.

import 'package:flutter_gen/gen_l10n/app_localizations.dart';

// ..
child: MaterialApp.router(
  // ..
  supportedLocales: AppLocalizations.supportedLocales,
  localizationsDelegates: AppLocalizations.localizationsDelegates,

We can also add helper extension context_extensions.dart to easily access localization strings.

import 'package:flutter_gen/gen_l10n/app_localizations.dart';

extension ContextExtensions on BuildContext {
  AppLocalizations get loc => AppLocalizations.of(this)!;

Now we can access the localized strings from the BuildContext like:

Widget build(BuildContext context) {
  var strings = context.loc;