- the prio of messages is now as follows for all themes (RL = realm localization, T = Theme i18n files): RL <variant> > T <variant> > RL <region> > T <region> > RL <language> > T <language> > RL en > T en
- centralize the message resolving logic in helper methods in LocaleUtil and use it for all themes, add unit tests in LocaleUtilTest
- add basic integration tests to check whether realm localization can be used in all supported contexts:
- Account UI V2: org.keycloak.testsuite.ui.account2.InternationalizationTest
- Login theme: LoginPageTest
- Email theme: EmailTest
- deprecate the param useRealmDefaultLocaleFallback=true of endpoint /admin/realms/{realm}/localization/{locale}, because it does not resolve fallbacks as expected and is no longer used in admin-ui v2
- fix locale selection in DefaultLocaleSelectorProvider that a supported region (like "de-CH") will no longer selected instead of a supported language (like "de"), when just the language is requested, add corresponding unit tests
- improvements regarding message resolving in Admin UI V2:
- add cypress test i18n_test.spec.ts, which checks the fallback implementation
- log a warning instead of an error, when messages for some languages/namespaces cannot be loaded (the page will probably work with fallbacks in that case)
Closes#15845
d543ba5b56