But I agree with the main point, will wait for FUTO Keyboard to support multiple simultaneous languages before I try it.
Apparently latest version of iOS keyboard allows for this kind of language mix ( heard about it second hand from an iOS user)
I switched from GBoard because it's predictions for Arabic were horrendous, made swipe typing unusable.
(I use Gboard with English and Korean and have to switch.)
Edit: there’s also a button to force the language if I want to override it. It also seems to read the text on screen or remember what apps use what language as it will auto-select the right language most of the time.
It also means things like you get all the diacritics from all of the languages when you long press.
I was studying French, while also working with several Polish people, so I set my keyboard to simultaneously English, French, and Polish, and then I was able to do French lessons without switching, and also able to write my Polish coworkers names easily.