I've seen GFI & II a million times and I can't decide. I am fairly fluent, but I might not sound too authentic if I were reading lines. Also, my Dad used to laugh at my Italian because I had the accents all wrong. I kind of picked up on that when Pacino and De Niro were speaking. So, even if they could speak Italian, they did not grow up in an exclusively Italian speaking environment, so their Italian might be halting. Also, they may not speak Sicilian dialect. In additon, De Niro is half Irish. It's a toss up.