I am an English speaker learning Mandarin and currently all the words in my notes on Mandarin are red underlined because they’re not English words (believe it or not).
Proposed solution
Allow a user to select multiple languages.
Current workaround
There are none really, I suppose the only workaround would be to change the language when I go to study Mandarin, but then all the English words in that document would be red underlined so its either or.