How do you localize a Flutter app?

The gen-l10n tool reads ARB files and generates typed localization classes. MaterialApp receives the generated delegates and supported locales. Flutter resolves the device locale against that list and rebuilds dependents when the locale changes.

{
  "greeting": "Hello",
  "itemCount": "{count, plural, =0{No items} one{1 item} other{{count} items}}",
  "welcome": "Welcome, {name}"
}

MaterialApp(
  localizationsDelegates: AppLocalizations.localizationsDelegates,
  supportedLocales: AppLocalizations.supportedLocales,
  home: const HomePage(),
)

• Never concatenate translated fragments to form a sentence
• Use plural and select messages so grammar works in every language
• Avoid fixed-width text containers where translation can expand
• Test right-to-left languages and use directional padding and alignment
• Format dates, numbers and currencies with intl using the active locale

Operational concerns

Translation is a content pipeline, not only a code change. Decide how keys are named, how missing translations are detected in CI, and how translators receive context. A missing key should fail the build or be clearly reported, not silently fall back in production without anyone noticing.