When the Predator said "What... the hell... are you?" to Dutch, near the end of the first film, did it understand the meaning of those words (and was it therefore genuinely asking that question)...? Or was it merely repeating what Dutch had just said to it, like a parrot mimicking human speech?
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.
They can very much speak and understand human language and are even capable of mimicking individuals to a T as well. When you hear them speaking English it's never their tech.
The 1st example is the Dutch "What the hell are you?". When he asked that question the Predator asks him the same question but has emphasis on the You. To me this is Dutch simply asking the Predator what he is and the Predator is asking Dutch what he is, because he turned the hunt around on the Predator making him the hunted. Something the Predator was not expecting since he made easy work of everyone else. The Predator is shocked to be beaten and does not see Dutch as ordinary. That's why I believe he knew what he was saying.
The 2nd example again is from the same scene. The Predator starts laughing which slowly starts to sound more and more human. His laughter did not start out as human sounding. This is the Predator laughing that he's going to take them both out, as well as making sure Dutch knows about it.
The 3rd example is from Predator 2. During the slaughterhouse scene when Harrison shoots the Predator and takes his mask off, the Predator calls him a "motherfucker", not from tech but his own mouth. I don't see anyone surviving long enough for him to mimic a situation like this. I believe he simply was annoyed that Harrison shot him and took his mask off.
The 4th example is from shortly after this scene when the Predator clearly says "Shit happens". I also don't think this is just coincidently said in the right moment.
The 5th example comes from the Alien vs. Predator movies. When ever we see them interact friendly with humans they tend to act like they know what we are saying, it does not seem like a situation where both parties have no clue.
The 6th example comes from pretty much all the movies. They tend to always have the perfect taunts ready, such as "help", "help me", and "over here".
The 7th example comes from the first two. Whenever they first interact with the human language they seem to study it, translate it, then mimic it as if they learning on the go. This knowledge of our language and translation technology was shown much more in the latest The Predator movie. As awful as it is, it showed us that they do in fact have are language on stand by. Though I hate that they took the predator ability to speak it away, Though it's possible he simply refused to learn it when he could simply just translate it through a machine like he did.
The 8th example which I almost forgot, when Harrison meets the other predators after killing the main one I guess you could call it. The Predator hands over an old pistol from the 1700s and tells him to take it. And I highly doubt he did not know what he was saying in that moment, as he even sat there a contemplates for a moment before turning back and giving him the pistol. Then one of the others says something I couldn't make out.
It's subjective of course, but I always interpreted that statement as a rhetorical question/retort.
Partly because of the context, and the slightly different intonation on the word "you" (which others have pointed out), but also because of the way it pauses to look Dutch over before it says those words, as if to suggest that his appearance was just as strange to it, as it's was to him.
There are certainly moments when Predators do appear to be merely replaying recorded audio of human speech out of context. When we hear them speak with their own voice though, it generally seems to fit the situation. Examples (from Predator and Predator 2):
Dutch: What the hell are you...?
Jungle Hunter: What... the hell... are you...?
Harrigan: You are one... ugly mother--
City Hunter: Motherf*cker!
Harrigan: Okay, p*ssyface... it's your move.
City Hunter: Sh*t happens.
The strongest evidence that at least some Predators have at least a limited understanding of English is probably the scene near the end of Predator 2, when the Elder Predator tosses Harrigan the flintlock pistol, and utters the words:
I find it very hard to believe that it didn't understand the meaning of those words, having spoken them in that context (especially as it wasn't repeating anything it'd been shown to hear).