These will need to be modified for the locale to use the correct
date formatting. Unfortunately, since the intl library does
not share the same flexibility for number formatting, the formatting
for an existing locale will have to be used as a substitute in
_NnMaterialLocalizationsDelegate:

For more information about localization strings, see the
flutter_localizations README.

Once you’ve implemented your language-specific subclasses of
GlobalMaterialLocalizations and LocalizationsDelegate,
you just need to add the language and a delegate instance to your app.
Here’s some code that sets the app’s language to Nynorsk and
adds the NnMaterialLocalizations delegate instance to the app’s
localizationsDelegates list:

Alternative internationalization workflows

This section describes different approaches to internationalize
your Flutter application.

An alternative class for the app’s localized resources