[jules]

The literal translation of "What do you want?" is "Wat wil je?", and this is considered impolite. You're unlikely to hear this from a Dutch waiter. You might hear "Wat wilt u?", but even this is rather curtly. The words "je" and "u" both get translated to "you" in English. "U" signifies respect.

[Fnoord]

"U" is the equivalent of "Sie" in German, but the Germans are far more gründlich (thorough) with using Sie correct. It instantly makes you feel more a respected customer.

[tankenmate]

In middle English and early modern English there was the distinction between thou and you (nominative case; thee and you for the accusative/dative case), the first is familiar and the second is polite. Obviously these days the familiar has been dropped and so indirect idiom takes the place of the honorific.