How to start learning Japanese
Go to settings, then go to learning language, then choose "I want to learn Japanese".
you can also make a new account, and choose that you want to learn Japanese.
I can still get into it using the menu next to my avatar, but I'd advise anybody who took advantage of the glitch and might still have access to be cautious. When I went to settings while on the Japanese tree, it sent me back to the new member screen and gave the appearance of having deleted my progress in existing trees. It hadn't, but I took a detour through a new-to-me tree just to be on the safe side.
It is interesting to get a preview, and the TTS sounds surprisingly good. However, I'd rather wait until it's properly released and not get lessons that consist of repeating 'one, two' twenty times.
Like wyqtor already said, I also suggest people not submit reports, as they might prove more of a hindrance than a help to the Japanese team at this stage of uncompletion.