Kanzi, a bonobo, seems to have learned to read the lexigrams used with other bonobos without being trained specifically to do so. So he effectively taught himself to read.
One of the experiments was Kanzi being separated in a different room, provided yogurt and them using vocalizations to get his sister to point a the yogurt symbol. In effect the vocalization seemed to have specific meaning.
He also learned some ASL from watching videos of Koko. It was never an intentionally taught skill, but it was something he learned. I will freely admit that Kanzi seems to be very much an outlier in terms of apes and language, but he does demonstrate that they are capable of using and learning language.