How do I switch courses???

I wanted to check out the new Russian Beta. When I joined Duolingo 3 years ago, you could go to the main page and look at other courses. It wasn't easy, for sure, but it could be done.

Now, there seems to be no way to switch or sign up for another language, while retaining your first language. I KNOW from searching this issue that people are working more than one course, but my main page on Duolingo is stuck on the German course and won't let me visit a mainpage or a new language at all.

What gives?