When writing emails in multiple languages, I noticed that the only language recognized by the Windows app is English (the primary language set in the app). This means that my emails are constantly full of red underlines, and I have no spell check help in other languages.
I have noticed that my wife does not have this problem on her Mac, and her desktop app automatically checks spelling in any language she has installed on her OS.
I also have all the languages I need installed on my Win OS, but this has no effect on Proton.
It would be very helpful to have this feature.