On a day to day basis I do use 4 different languages, sometimes even mixing them in a single conversation (i.e the other person is bi/trilingual too). For me the autocorrection is only a distant dream and will probably remain so for a long time.
Human language is actually just one vast system, it isn't best understood as a bunch of nicely compartmentalized independent languages. So in a way it would actually be more wrong for an AI model to insist that "Beacoup money" isn't a reasonable thing for the user to want to write, just because those two vocabulary words don't co-exist in a single defined language. The user may or may not know that, but they certainly don't care.
It looks like it uses all the dictionaries so suggestions appear from all languages for every word you're typing.