I completely agree. I speak two languages regularly (English/French) and I also find it to be a pain point.
It's something that I hope we can address over time with Minuum. Certainly the first step will be making it really fast and painless to switch languages.
We've also considered having a quick way to disable auto-correction/disambiguation on the fly.
Do you have a favoured solution? Sounds like maybe simultaneous language support doesn't quite cut it for you.