Viewing your profile, some posts/comments are unspecified, some are Français, some are English.

The languages in 'settings' determine what you see. We all see 'unspecified' stuff, but if you don't have Greek ticked in your settings, you won't see posts made in Greek. (It seems impossible to actually untick 'unspecified' and for the change to go through.)

If depends on what you're using to post (what front-end, app, etc), but they also typically determine what languages appear in the drop-down selection, factored by what languages the Community you're posting in accepts. It's what you choose in this list, the one that's part of process of submitting a comment or a post, that selects the tag for a particular post. It likely defaults to whatever language you made your last post in.

So yes, if you have 'english', 'francais' in your settings, you'll be able to choose between the ones the communities accepts. If it accepts neither, you'd have to choose 'unspecified'.