All my progress is gone
I recently updated duolingo and after the update all my progress was gone. I have to start over now. Help!
This is only relevant if you actually changed your display language before. E.g. you previously learned English or German from Spanish, and now you are learning German from English.
Go to Home, then click on the little round flag to the right. (Not the top one with your name close to it.) You will get a selection box in which you can make selections such as "I want to learn German (I know English)" or "Quiero aprender inglés (yo sé español)". Here you can choose your interface language (= language of departure) and the language you are learning, simultaneously. Use the button on the top right to confirm, wait a few seconds until the interface has updated, and then verify that your old progress is staill waiting for you. You can switch as often as you want.