We use Transifex to manage our translations. To get involved, you'll need an account on Transifex. You can dive right in on our Transifex project page, but we also encourage you to go through our full onboarding procedure.
The way we have Transifex set up is that anyone can join one of our language teams as a translator, and you can start translating strings. Someone else will review your translations before they go live.
Transifex lets you request new languages if you don't see the one you're interested in.
We need 50% of the strings translated for a language before it gets deployed.
Since we are open source you can find the context for any string, though it takes a few clicks, and you have to be comfortable reading source code. On the “Context” tab for a string, look for “Occurrences.” It should look something like this:
Then find the file by browsing our source code to see how the string is used.