I added English for Chinese speakers, and everything else got wiped out!
I had been working my way through all the current languages for English speakers: Italian, French, Portuguese, Spanish, and German. I was around level eight in all of them. Just for fun I subscribed to English for Chinese Speakers. Now all my other languages and histories have been erased from my profile, and everything on my phone and on the Duolingo website appears in Mandarin. Is there a way to get back to where I was before?
This is the normal effect when you change to a course starting from a different language. Don't worry, nothing is lost. It's just a very annoying usability problem.
Go to "Home", then click on the little circular flag on the right. This takes you to a page where you can easily choose between all available courses, regardless from which language they start. Pick any of the courses for English speakers, and confirm. After a few seconds the interface will be English again (don't click around earlier) you will see your progress in all courses starting with English. By almost the same procedure you can go back to Chinese and see your progress in English for Chinese speakers again.
The problem comes up all the time and I am sure it would have been solved a long time ago if it were an easy fix. Unfortunately it isn't. Luis von Ahn once explained the problem. Apparently, Duolingo has built everything on a software framework that deals with the different user languages. Since this isn't flexible enough to solve the problem, it must be thrown out or extended. That's a massive change with the potential to break the entire site.