Lets break it down.
1. Predators don't speak English.
Yes i know they can do vocal mimicry, Buts that's like saying a parrot can speak English. We don't think they have any idea what they're saying. Dutch may have well said "Ravioli ravioli give me the formuoli" and it wouldn't have made a difference.
2. Where does the code come from?
Dutch. He said "He didn't kill you because you weren't armed - No sport." Which is making a huge assumption, Dutch doesn't know this space monster. He's never sat down with him and had tea with him whilst discussing the philosophy of murder.
But there is one reason that the idea of an Honor code still stands
3. COMIC. BOOKS.
Yes that's right. I went there. Let me clarify. IF YOU HAVE TO READ ANY OF MY POSTS READ THIS.
In the AvP universe, Predators tend to follow an honor code. This code may vary from clan to clan much like our own ideas of morality. We know this from the AvP comics. Which are, Let me remind you. More canon than the films in the lore of AvP, Since they came first.
In the PREDATOR universe, We do not know currently if Predators follow an honor code. We simply made the assumption that they do from AvP which is not cannon in the predator universe.