Flutter: How use flutter_localizations in package

Question

I plan to move some common function / page to "flutter package"

But how to handle localization in these package ? I try to follow step https://docs.flutter.dev/development/accessibility-and-localization/internationalization

But it seem app-level localization, How to add localization in submodule/package ?

Update:

I tried to add flutter_intl / flutter_localizations in submodule, let it work like app-level. I also add module delegate in localizationsDelegates like this

    return MaterialApp(
      localizationsDelegates: const [
        S.delegate,
        module_a.S.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ], ...

After test, here is result:

1. it can build.
2. but it seem not use submodule's translation. it always show english at this case.
3. If I copy translate items from submodule to app, it seem work. it look like app translate string will override submodule's translate string

Am I use correct way to implement translation in flutter sub-module ?

Answer 1

I am not able to test your code, but I hope this helps.

Regarding

2. but it seem not use submodule's translation. it always show english at this case.

As stated in MaterialApp's documentation:

///  * [supportedLocales], which must be specified along with
///    [localizationsDelegates].

If I do not specify the supportedLocales, my app is only shown in english.

Regarding

3. If I copy translate items from submodule to app, it seem work. it look like app translate string will override submodule's translate string

I think you are right, that the first S.type, in this case the S.delegate, is selected, because both S.delegate and module_a.S.delegate have the same LocalizationsDelegate.type=S.

Something similar can be found in MaterialApp's documentation:

/// Constructing a [MaterialApp] with a `FooLocalizationsDelegate` overrides
/// the automatically included delegate for [MaterialLocalizations] because
/// only the first delegate of each [LocalizationsDelegate.type] is used and
/// the automatically included delegates are added to the end of the app's
/// [localizationsDelegates] list.

---

I split my flutter project into different packages, and the solution I choose is to generate a separate delegate class for each package (module).

Example for a module l10n.yaml:

arb-dir: lib/l10n
template-arb-file: app_en.arb
output-class: moduleALocalizations
output-localization-file: module_a_localizations.dart
synthetic-package: false # important, if you want to import the delegate in another package or app
output-dir: lib/l10n/generated # this is optional, if synthetic-package=false and not stated, defaults to arb-dir location

I set output-class and output-localization-file to the class and filename I want to use for the module. The delegate is added as to the [localizationsDelegates] as usual.