From what I understand, a lot of cat vocalizations to humans like meowing and purring are primarily things kittens do that cats later stop as they grow, to communicate with their mother. They learn to continue using such vocalizations with humans because humans don't understand their body language as readily, so they discover that, for example, a certain type of meow when hungry might remind a human to feed it, and keep doing it. This also means that the meaning of a given sound is somewhat specific to a given cat, rather than some sort of universal cat language. Or at least, this is what Ive read