Upcoming changes in registration process
Fragment of a discussion from Translation UX feedback
No, they can follow the same process. I think they can also add example "translations" to qqq if they don't know any other language? You're right about translators for new languages, this just happened with User:Paul Beppler (who was confused by not having the right to post new threads, because sandbox users are restricted) but Nike told him to translate in whatever language and I approved the account.
Personally I hope normal account registration won't be disabled, because the new process covers only a subset of all the possible cases; but anyway addition of new languages is basically frozen currently, we need a revamp and we should also update the docs on how to get appropriate permissions to write LQT threads.