This isn't intended as a correction, more of a relevant FYI:

Primate's ability to sign has been wildly overstated. Koko the Gorilla was a lot closer to a chicken playing tick-tack-toe than Cesar from Planet of the Apes.

Like the chicken, Koko's ability seemed dependent on the presence of her trainer. For example, her trainer would often explain that a nonsense word or sentence that the animal signed "rhymed" with what that she intended. Of course "rhyming" in sign language is a thing, but it works completely different than it does in speech.

Chomsky was right, language is human firmware and cannot be taught to our cousins. The history of our effort to do are mostly stories of animal abuse peppered with some human tragedy.

https://www.youtube.com/watch?v=e7wFotDKEF4