The Three-Fifths Comprimise showed that the definition of a person can depend on quite a lot of things.
Right. The philosophical notion of personhood is a messy area. In the context of slavery, it relates to
legal rights (whether slaves should have the right to vote, for example) but in the context of ethics, it's fundamentally about whether a being has
moral agency. Nobody ever denied the fact that American slaves had moral agency—the question was regarding their rights.
In the Star Wars universe, it's pretty obvious that Jabba the Hutt has the capacity to act morally, which would count him as a person, in the ethical sense. Even though he's not a very nice, um, person, we wouldn't feel good about torturing him because we would intuitively understand that he is subject to our own moral act of torture.
I don't think this is true for droids though, however intelligent they may be. It's hard to imagine R2-D2 going to trial for murder. And you would certainly feel much worse about torturing Chewbacca than you would C-3PO, even though 3PO is fluent in over 7 million languages and Chewie just one.
Anyway, what we can say is that in the legal and ethical senses, the notion of personhood is not fundamentally related to the human species. There are many philosophers who would even count your pet hamster as a person, given that it deserves some level of legal protection. And although I've never heard of anybody talk of legal protection for machines yet, I agree that with the rapid progress of complexity in AI, it may be something we need to think about before the end of the century.