I fail to see how this is rude in the least. I have friends who regularly post in French, Spanish, Georgian, Hebrew, Danish and Swedish, in addition to English. If I really want to know what my friends are posting in Georgian, Hebrew, Danish or Swedish, I can use Google translate. I myself sometimes post in my second language (French), which a substantial portion, though not all, of my friends can read. It never occurred to me that I might be "excluding" people.
I say you're fine, OP, and your friend is rude to try and dictate what you post.