Copying primary language translations to region subtag

In general, this is not necessarily wrong: there might be some applications which don't handle language fallbacks. In the "MediaWiki" namespace saving an identical message is (still?) prevented, but by MediaWiki core itself rather than Translate (perhaps only for locally installed messages?).

In general it should be possible to add a checker warning translators about the identical messages; usually best done by someone with intimate knowledge of the group/project.