When your cat meowing and you meowing back to him, is he understand hooman language?
Actually, in the sense of the noise you make having a specific meaning, probably not. But in the sense of you trying to get his attention and deliver something, absolutely yes.
Imagine you are having a conversation with someone – you speak only English, he speaks only Chinesse. It will be very easy for the two of you to communicate in non-verbal ways (smiles, nods, handshakes, pointing) but your words will be mostly meaningless to one another. You will likely be able to tell each other your names, with the assistance of pantomime, and even if he does not say your name perfectly you will understand when he produces a close approximation and respond accordingly.
It is pretty much the same as when we try to communicate with other species of intelligent animals. Our tone of voice, body language, and mental state such as happy, excited, and even angry have much more to do with the conversation than our words. Certain verbal sounds like (No, Food, Out) easily become paired with specific actions and the animal quickly grasps the connection between the two.
I suppose the cats generally ONLY meow to communicate desires and intentions to human beings. The wildcats don’t meow, except when mother cats try to get the attention of their kittens – adult wildcats are virtually silent save for hisses, screams, and also growls. The meow is essentially a construct created by cats to make humans aware of catly needs. Amazing, isn’t it? Its only common courtesy for us to try to understand what meows mean and replicate them, since the cats went to all that trouble to learn to talk to US!
I tend to talk to Milky in hooman words, and while he has NO idea what I’m saying, he understands by the tone of my voice what mood I’m in, and responds accordingly. Occasionally I will indulge in “cat-speak” (purrrs and groans) during cuddle time or grooming sessions when he is being especially affectionate and receptive, and when I purr at him and he ramps up his purrs to the point of doing structural damage to the house. So while my “purr” isn’t the same as him, but he understands it’s meaning and responds in kind.
For being the two completely different species with entirely separate evolutionary paths, I think that this kind of thing is nothing short of miraculous.