I know Italian, and I don't stutter when I speak it, but I am not nearly as fluent as I am in English or Portuguese, so I assume it is because I speak way slower. I didn't grow up stuttering, I moved to the US when I was 14, when I returned to Brazil to visit family when I was 20, it was the first time I've ever stuttered for real, as soon as I got the airport. I moved back to the US for many years, now that I've returned to Brazil, I am going to a hypnotherapist and a speech pathologist, my improvement has been noticeable but not even close to being "cured".