again, if the person who is making the post doesn’t change the setting, it won’t get filtered. if they type a message in German but the post’s language option is set to English (which I think is the default on some major instances), it won’t get filtered out.
you can usually check what their post’s setting is by starting writing a reply to them, as the language option of your post will switch to the one they post in.
then go for it.