I think it's pretty straightforward. He's a caricature of black people. His speech pattern is definitely influenced by Ebonics, his dress, and that of the Gungans as a whole, seems related to Caribbean modes. Finally, a great deal, if not all, of the Gungans are portrayed by black actors. It's a pretty clear he's as much a caricature as Al Jolson in The Jazz Singer. It's equating blacks with "the Other" by literally making them alien.
And, if you want to argue that "oh, well, that's sort of an accident, or maybe Lucas doesn't mean it to be taken that way" I'll say this: I'm sure it was an accident, and I'm sure it wasn't meant to be taken that way. But as aliens, evolving entirely separately from humanity, there's absolutely no reason they should have speech patterns even remotely resembling ebonics.
Lastly, the issue is not even really that Jar Jar is a caricature in his similarities. Its that George Lucas then makes the blunder of having what essentially boils down to "the black character" be a bumbling stupid idiot who succeeds solely by screwing up SO BADLY that he comes out the other end of failure into grand success. Also, to really drive home the point, Lucas makes the Gungans spear and catapult wielding jungle people.
