Unfortunately, you loose progress when you switch languages. When you switch languages in Codecademy, you can think of it as starting as a new user. Your progress hasn’t been lost—if you switch back to the language you started with, your progress will still be there. I know this is confusing, and we’re actively working on a solution to sort out this issue. I recommend sticking to one language so that your progress remains consistent.
Also, when a user creates an account with an email address then uses a third party authentication account (fb, google) to log in, and their authentication account is connected to a different email. Which means that they end up creating two accounts and the second account doesn’t have any of their progress.
Still seeing errors? Comment below or please report it and include as much detail as you can on our forum here: http://discuss.codecademy.com/t/language-errors/8716g
-Codecademy Community Manager