Account language has changed
My whole account is suddenly in German instead of English. His can I change this? Also all my progress in learning French is gone.
Did you start doing a reverse tree? You just need to reverse the process. Go to the flag on the header band at the top. Pick Add a new course, select English as your base language and add French/German/whatever for English speakers.
Happened to me too, I wanted to see how learn english looked, but then my spanish lesson went away! I got it back by deleting my learn english. If you were't messing around with the languages (similar to what I did) then just do the previous steps then change your password for safety and so your account doesn't suddenly kaboom.