If you are into Chinese, Korean or Japanese, HelloChinese and YuSpeak are good specialized duolingo clones, exceptionally better than duo. You will still need StrokeOrder or WrittenChinese websites though

I take my words back, YuSpeak sucks balls. There is Ling if you want, but it goes full brutal and without mercy on you, and it's not for you if you don't know hiragana and katakana. Ling also has Serbian and Mongolian btw

Mongolian