I'm talking about new languages, which haven't been launched yet, because they don't have enough text to record yet.

The actual method to contribute to them is finding Mozilla's internal translation tool, proposing translations, then finding a Mozillian to approve them. Then there's an obscure webapp for sentence submission and voting, but it doesn't give any feedback whether sentences you've submitted were accepted or went to /dev/null.

(you see people struggling with easiest things, because you assume people struggle with easiest things, rather than that you've misunderstood the problem.)