MGNLUI-4240 introduces the isMessageKey method as protected on AbstractFieldFactory level.

ComponentSelectorFieldFactory and TemplateSelectorFieldFactory previously contained the same method—yet as private. This is binary-compatible but those factories need to be adjusted whenever pages depends upon UI 5.5.6+ (methods may simply be removed if similar).

This method checks whether an @I18nText config property is likely to be a message key (from key-generators) or a proper translation. As definitions are proxies to the translation-service, this method is often the only choice to know if a translation exists or not.

Some UI components may decide not to display the unresolved message key when such translation does not exist (like for the placeholder text in the aforementioned UI ticket, or here for template titles).