I referred to this NGM article in another sub-parent comment here, but I think it contains very relevant on-topic animal intelligence language-related insights, so posting a link and a couple of short excerpts from it here:
Under Pepperberg’s patient tutelage, Alex [a parrot] learned how to use his vocal tract to imitate almost one hundred English words, including the sounds for all of these foods, although he calls an apple a “banerry.”
“Apples taste a little bit like bananas to him, and they look a little bit like cherries, so Alex made up that word for them,” Pepperberg said.
[...]
[...] because Alex was able to produce a close approximation of the sounds of some English words, Pepperberg could ask him questions about a bird’s basic understanding of the world. She couldn’t ask him what he was thinking about, but she could ask him about his knowledge of numbers, shapes, and colors. To demonstrate, Pepperberg carried Alex on her arm to a tall wooden perch in the middle of the room. She then retrieved a green key and a small green cup from a basket on a shelf. She held up the two items to Alex’s eye.
“What’s same?” she asked.
Without hesitation, Alex’s beak opened: “Co-lor.”
“What’s different?” Pepperberg asked.
“Shape,” Alex said.
Article:
http://ngm.nationalgeographic.com/print/2008/03/animal-minds...