Important: #108783 - Backend user language default changed to "en" 

See forge#108783

Description 

The backend user language field (be_users.lang) historically used default as the value for English. This has been changed to use the standard ISO 639-1 language code en instead.

The language key default is still accepted for backward compatibility with custom code, but can no longer be selected in the backend user interface.

An upgrade wizard, Migrate backend user language from 'default' to 'en', is available to migrate existing backend user records.

Impact 

  • New backend users have en as their default language instead of default.
  • Existing backend users with lang=default should run the upgrade wizard to migrate to lang=en.
  • In general, code that uses default as a language key (e.g. custom instances of LanguageService) will continue to work, as default is still mapped to en internally.