Well it's not in a chimpanzee's nature to try to transmit useful information to someone else, so they don't need language.
Despite their intelligence, apes not only do not talk—they will not even point things out for one another using their hands (Tomasello 2006). Tomasello (2008:5) comments that when a whimpering chimpanzee child is searching for her mother, it is almost certain that all of the other chimpanzees in the immediate area know this. But if some nearby female knows where the mother is, she will not tell the searching child, even though she is perfectly capable of extending her arm in a kind of pointing gesture. She will not tell the child because her communicative motives simply do not include informing others of things helpfully.
