How do you say "Who are you?" in Japanese?

"Who are you?" is literally translated into "anata wa dare desuka?" In casual spoken Japanese, we say " anata dare?" In polite spoken Japanese, we say " dochira sama desuka?" Dou itashi mashite ( you're welcome), in advance:D

non-polite : あなたはだれ？　(anata wa dare?) Polite: どちらさまですか？ (dochira sama desu ka?)

This is impolite, but literally 'Who are you?' It's "(Anatawa) dare desu ka."

It's very rude so it must be translated in to same way as Omae wa dareda or Anta dare? If you need to be more polite translation, It would be Anata wa dare desu ka? You must state you as Anata, Omae or Anta as subject in this case anyway distinctly.

For non-polite is Kimi wa dare?(君　は、だれ？) Very polite word is Anata wa dare desuka or dochirasamadesuka?(あなたは、だれですか？/どちら様ですか？

omeh dare dayo? or omeh dare yo? or jibun nanimono yo? or antah anoko no nan nanosah?

dochira sama desu ka? if you are answering phone,

dare des ka?

<anata wa> dare desu ka is impolite.. <anata wa> donata desu ka is better.