WordsTool supports 21 languages. Any of them can be the language you teach, and any of them the language you teach it through — you pick both when you add a language pair.

Arabic, Chinese, Danish, Dutch, English, Finnish, French, German, Hindi, Icelandic, Italian, Japanese, Korean, Norwegian, Polish, Romanian, Russian, Spanish, Swedish, Turkish, Welsh.

A pair, not a language. Every set, every word and every task belongs to one pair — English through Russian is not the same shelf as English through Spanish. Add as many pairs as you need in Settings → Education.

Pairs belong to an account. If you have both a teacher and a student account, each has its own pairs; adding a pair on one side does not add it on the other.

Pronunciation and suggested translations are offered for the languages above; how much a language gives you depends on what the voices and dictionaries have for it.