It also does in Spanish, it's a (rather old, but still used) shortened version of "retard" (from "mongólico", originally used to describe people with Down's syndrome).
Same in Swedish
Same in most languages, but there's also Emperor Mongo in Flash Gordon stories, definitely alluding to Mongol conquering hordes.
Most languages would be a stretch, there are over 7000 languages in the world.
Lose the O and it's also a nasty piece of British slang meaning the same thing.
It’s funny. Someone I used to know from Scotland is/was a software tester by day. She went mental about the name of their companies new DB. All over social media. “Derogatory, backwards”
This is true in virtually all languages, as John Langdon Down used it to refer to the syndrome he first characterized, that today instead bears his name.