Please add language support to the mail clients. I regularly compose mails in different languages. The spell checker just underlines anything that's not in the account's "Default language".
I object to the word "Default" here, since it's the only place where you *can* change the language.
This is basic functionality, that should be there before any of this AI stuff that I don't need.

Use grammarly…is better then apple and google and is free somehow

I fully support this suggestion. The lack of this functionality in Proton Mail is one the things preventing me from dumping Gmail altogether

Strongly agree with Eric's suggestion. I switch back/forth from platforms that will correct simply things (e.g., change "teh" to "the" or capitalize "i" as the first-person pronoun). I either spend time reviewing for such simple things or I send what appears to be a poorly fashioned message.