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.
The glitch now appears to have been fixed; when I try to switch to Japanese it cuts to the Duolingo splash screen and forces me to choose another language. Furthermore, Japanese is no longer selectable via settings.
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.
To those stuck in the 'Intro' skill, even changing and accessing through the URL-changing, this will not unblock the rest of the three. So I recommend to do the Checkpoint test, that's how I unblocked it:)
すごい！I would be happy to help the team by submitting reports, but I am not sure we are supposed to be able to join the course, so I will refrain until further notice from the team.
Awww I can't believe I missed this opportunity again...
I hope this glitch happens again :c
It was a glitch which they have sorted and now it is not possible.
You will just have to wait until they release into Beta.
It works fine.
Thanks for pointing that out. :)
Edit: And no longer works, as far as I can tell.