Speaking as a total ignorant from a coding perspective. But I guess that wouldnβt be the hard part, considering that most of Duolinguo is just boxes and text inputs. How difficult it is to create a database of competent linguists with an efficient training who can progressively enhance your understanding of languages?
Try taking a break for a month and see how much you actually remember. In my experience it was depressingly little, and Iβm not generally bad with languages at all.
I think that would go for most learning methods. When you donβt practice a skill youβre always going to get worse with it over time, especially if it is a language.
After a certain point you should be able to retain a language for more than a month - after youβve attained B2ish level Iβve heard.