Plural ICU expressions depend on the locale (different languages have different plural forms). Until now the locale was hard coded as `en-US`.
For compatibility reasons, if you use ivy with AOT and bootstrap your app with `bootstrapModule` then the `LOCALE_ID` token will be set automatically for ivy, which is then used to get the correct plural form.
If you use JIT, you need to define the `LOCALE_ID` provider on the module that you bootstrap.
For `TestBed` you can use either `configureTestingModule` or `overrideProvider` to define that provider.
If you don't use the compat mode and start your app with `renderComponent` you need to call `ɵsetLocaleId` manually to define the `LOCALE_ID` before bootstrap. We expect this to change once we start adding the new i18n APIs, so don't rely on this function (there's a reason why it's a private export).
PR Close#29249
This fix is for the issue below when compiling I18N Angular apps using closure.
For certain locales closure converts the input locale id to a different equivalent locale string. For example if the input locale is 'id'(for Indonesia) goog.LOCALE is set to 'in' and the closure locale data is registered only for 'in'. The Angular compiler uses the original input locale string, 'id' to set the LOCALE_ID token and there is a mismatch of locale used to register and locale used when requesting the locale data.
The fix is for the closure-locale.ts code to register the locale data for all equivalent locales names so that it doesn't matter what goog.LOCALE is actually set to.
PR Close#25867
Olivier Combe
Daniel Ruf
Vikram Subramanian
Victor Berchet