There is no point in dealing with the complete list of languages for the spell checking options in the email window. It should be configurable what languages you want to see from the email options. Even more, it should be possible to uninstall any language.
Not all languages are listed there; just a few to get users started.
If you want to remove any of them, you can. You will find the files in C:\Program Files (x86)\eM Client\Dictionaries\
No, I get all the languages. And I haven’t find a way to remove them in MacOS. And it is very annoying, I write in 3 different languages, and each time I need to switch to the right language (no auto detection), I need to search an unneeded long list of languages I don’t speak and I won’t ever use.
Oh, you’re on a Mac.
The spell-checking is offered by macOS not eM Client. You’ll need to see if you can disable them in your OS.