Don't hide already-joined languages on the "Join" page
We had an issue where a translator used a "Join" page link to sign up for the German translation team, but somehow forgot that they had done so.
When they went to the "Join" page a second time, German was not an option in the already-allowed languages (because they were already a member of the team), and also it was not an option in the "suggest a new language" input, because it already had a team formed for it.
It took us a while to figure out what was going on!
It would be clearer in the UI for the already-joined languages to still be shown, but be grayed-out or something to that effect, such that the person can tell they have already joined that language team.