They can vocalise more than just their names, so if anything, they’re Digimon.
I don’t think this is true, there’s some Pokémon that speak normal language like meowth, lucario, legendaries etc…
Every human can talk because they were taught. Meowth couldn’t talk until he taught himself how(to try and impress a girl meowth 😭). Humans don’t teach their Pokemon to speak, and most don’t have the inclination to teach themselves. So for all we know every Pokemon is capable of human speech if they were taught.
Idk i think that’s just how Pokemon moo or whatever and the names are onomatopoetic.