You got a good response about this already, I just want to add to it.
I am not sure about the folders, if the FOLDERS on your partition are named in other language than English I am not sure this will help (they would have to be renamed in your filesystem), but I made this little tutorial specifically for KDE plasma and dual languages.
Maybe the folders have English names, it’s just that you see a different language in the desktop, and then this could potentially help)
But I advice you to get your GPU in order before fixing your language problem.