This Wikipedia link says,
Sign language and computer keyboards are used in primate language research because non-human primates lack vocal cords and other human speech organs. However, primates do possess the manual dexterity required for keyboard operation.
If chimpanzees lack vocal cords like humans, how was Caesar able to speak in the movie?
The cognitive ability of Caesar to learn language is taken care of in the movie. But the physical ability of Caesar to speak is unclear to me.