Duolingo offers language courses in 39 languages, including Arabic, Chinese, Czech, Danish, Dutch, Esperanto, Finnish, French, German, Greek, Haitian Creole, Hawaiian, Hebrew, High Valyrian, Hindi, Hungarian, Indonesian, Irish, Italian, Japanese, Klingon, Korean, Latin, Navajo, Norwegian, Polish, Portuguese, Romanian, Russian, Scottish Gaelic, Spanish, Swahili, Swedish, Turkish, Ukrainian, Vietnamese, Welsh, Yiddish, and Zulu.
Duolingo also offers foreign language instruction for non-English speakers, but these options are more limited.