Afaik it has never worked right. If you properly set your post to English, it would hide your post from everyone who didn’t have a language set (so everyone).

The way it should work is if you don’t have languages set in your profile it should show you all languages. If you do have a language set, it should show you those languages AND undefined.

Then you’d be free to specify the language of your post without hiding your post from 99.9% of users.