It works for Esperanto (which is arguably the easiest language to learn). I completed the Duolingo course in a month, then I could read Gerda Malaperis in thre

It works for Esperanto (which is arguably the easiest language to learn). I completed the Duolingo course in a month, then I could read Gerda Malaperis in three days and Vere aux fantazie in another month, then I could read suitably advanced stuff. For other languages I tried, it didn't work at all, but it could be because of my lack of patience.