breaking up MediaWiki message group to smaller projects

Not going to happen. We have MediaWiki most used, all of core, meta message groups and hundreds of different other extension groups. Yes, it is a lot of work, and it has to get done. Please consider "just translating" instead of talking about (and spending time on) how to make the translation process even more complex in itself or meta-engineering the few thousand messages that exist.

Of course it has to get done. Breaking it into meaningful groups will make getting it done easier.

I'm talking only about MediaWiki, not about the extensions.

I'll reply once more: this discussion is done and translator's time is best spent on translating. I'm sorry, but this is not open to discussion.