"Kdo z vás umí nejmíň jazyků?"

Translation: Which one of you speaks the fewest languages?

[vor23]

Sorry, but "the least languages" is not correct English. Because languages can be counted, the right phrase to use is "the fewest languages."

[Stephen900455]

I agree that 'fewest' works better here but 'least' can be used for countable objects. Example: Peter, Paul, and Mary have 1, 2, and 3 beans, respectively. Peter has the least.

[Paul378887]

Could “který” be used here in place of “kdo” and still have the same meaning?

[VladaFu]

yes