Does the Predator simply repeat what Dutch has just said "what the hell are you?" Or is it asking him the same question back?
He's taunting Dutch
There are a few times in the film where the Predator records the voices of humans.
It seems to use them as a taunt rather than a lure. The one time that it could have conceivably been using a voice to lure a human was when he replayed Mac's "over here" to Dillon. But Mac was dead at the time, so it frightened Dillon rather than lured him over.
There's no indication that the Predator can speak or understand any human language. When Dutch asks him that question, the Predator doesn't understand it. Why he plays it back is open to interpretation, but I would argue that it's a taunt or an attempt to "tell off" / rebuke Dutch.
Since he follows it by detonating a large bomb (also, playing back Billy's menacing laughter), trying to kill Dutch, I would imagine he's saying communicating something like "you may have beaten me, but you're going to die too."
Given the inflection the predator places on the word you (which Dutch does not), it's not mimicry, it's equal parts taunt and complete understanding.
Dutch's sentence ends with a period. The predator's ends with a question mark.
Dutch: What the hell are you.
Predator: What. The hell. Are you?
There's no indication of how the Predator can speak or understand English, but he sure does know how to raise the pitch on the last word of a question that's thrown right back at its asker.