Belgian born and raised. I had 3 keyboards on my phone, all QWERTY (I can't stand AZERTY) but with different spell checks (Dutch, French & English)
When iOS 18 came out with this feature I turned it off, because it's not smart enough to infer context (at least when I used it, maybe it got better?), and messed up autocorrects.
I just use Romanian and English. Sometimes in the same phrase. Eventually it gave up and seemed to adapt enough to what i tend to type to not annoy me every time I send a message.
But then, that was the behaviour even before iOS 18 when I had two keyboards installed. It just took it longer to give up and accept both languages on both keyboards :)