Thanks so much everyone! I didn't expect to wake up this morning and find it almost finished. I've also added the four languages that have been requested: Catalan, Czech, Sinhala (Sri Lanka) and Ukrainian.
We can nominate reviewers for each language who can approve or reject each translation. During my day job I work with a lot of people who have moved to NZ from different countries so I'll get them to check over the languages that they know and see if we need a review process.
I happen to work with a Pole who also translates on the side, she's volunteered to take a look as well. Dziękuję!
I've just played around with this myself and it seems you have to leave the first language before you can join the second. No idea why, a morning's worth of Googling hasn't made me any wiser.
So you have to go to Portuguese (Brazil), click on "View members", then the "Leave" button next to your name. Then the "Join team" button will appear on other languages.
I'm pretty sure it's something to do with the way I've set up the project, it is puzzling why you'd be locked down to only one language.