--Well, yeah, I mean... Pokemon are pretty damn smart.

I know a few straight-up know how to talk-- or at least write-- like a person. I had an entire extended conversation with someone's Snubbull about literature once.

_{[... Okay, she'd been retelling the story of Watership Down in her own words, which had included a lot more modern slang and irreverent commentary, but hey, it counts! And Steve Buscemi had LOVED it.]}

They can definitely understand you if you talk to them, in any case.