Lets look at the facts, let's say that lantern guy in twilight princess asks you if you want lantern fuel, you have to select the yes button or no button. If the lantern guy understands link, it means he communicates in a way. Now since zelda is third person, you can see he's not doing any sort of sign langauge. Now if you make link jump of a ledge, he will scream in pain. Or if you do certain attacks, link will do a battle cry like "Kya!". I think that's enough to say. He does speak after all.