Years ago I studied Chinese on here and I wanted to reset it. I deleted it in the settings page but it is still not gone from my account. The language is no longer on my list of languages in the settings but I can still switch to it in the normal way. See here for example
All my old stats are still there when I open Chinese.
I did not, but I think the issue lies in another castle. When I logged onto the website today from my phone, I got a notification (in the form of those little green pop-up boxes) that Chinese has been deleted and it is now gone. Between the time that I deleted the language and this pop-up appearing, I did not get any notifications for messages on the forum. The pop-up appeared around the time that I got all those notifications at once, including tens of emails about them.
Anyway, I don’t know what happened. It might end up being a mystery that we never know the answer to and we are just going to have to find some way to live with that.
By the way, I can’t imagine that there is any good technical reason why deleting a language should mean that one’s progress in that language cannot be recovered. It would suck so bad for a user to lose years of progress because they clicked the wrong language. I think if one deletes a language, when they open that language again they should be asked if they want to restart where they left off or start from the beginning.