I can tell you that github.com/jeroenhd/roest was all done manually.

If I'd used AI, I probably would've included grammatical gender for nouns.

The Russian version seems to be handcrafted with humor

It definitely was.

I don‘t think so. At least the french one is quite old and was discussed here before AI was in wide use: https://news.ycombinator.com/item?id=28490935

I remember that many of the other languages popped up a little later.

I doubt it. Rouille uses a very simple "word to other word" map that anyone with an hour of free time can fill out for their own language.

The implementation is also rather inefficient, but it's not like such a translated macro will be used for anything serious.