I see this as something for 5.3.
Basically, combine all the localized messages for the core library into a single message catalog. This includes content that is currently in component message catalogs, as well as content in validation message catalogs.
The core message catalog could be contributed to the global message catalog, ahead of the applications' message catalog. This would allow an application to easily override any of these messages from the core library.
It would also make adding and maintaining localizations easier, as there would be just a single file's content to be translated.
It may be a good chance to up∂ate the various message keys to be unique and unambiguous. Possilby adding a "t-" prefix as well.