"Proč musím umět víc než jeden jazyk?"

Translation: Why do I have to know more than one language?

[paulk1011]

Seems like "Why do I need to..." should also be accepted.

[BoneheadBass]

On the English side, yes, it does -- and I've used it and been wrong, too.

But on the Czech side, the verb used is "muset" (to have to), rather than "potřebovat" (to need). So my GUESS is that there's enough difference in meaning between them that only the first is acceptable in this context.