Guess you don't know the meaning of "4th generation" meaning His family would've immigrated from Europe to America in like the 1700s. Also, you're trying to deviate from the point which was originally part of his "hispanic" accent because he comes directly form Spain. I was saying his ancestors could have, and he wouldn't have kept their accent if being born in America.
Niko and Roman weren't born in America I'm pretty sure Jacob wasn't either.Also, I'm pretty sure Packies parents or grandparents were raised in Ireland, so they infulence him and his culture. The Yakuza and Triads are organizations of people that was created in Japan and other parts of Asia where they are centred. The branches in America are just expansions of their business.
EDIT: And still, the American triads (Woozie) and the McReary family that were born in America have American accents, not Chinese/Irish accents.