I configured several system languages, but I get red underlined text when the word is not in the primary (first) system language. I use a 3rd party keyboard and am on Android 7.1.2 Nougat.
As the user interface for changing underlined words is not from the keyboard itself, but from the system, I ask myself:
Can I configure the system spell checker keyboard-independent to accept multiple languages simultaneously?
I want to keep using my 3rd party keyboard (Messagease).