When I was first learning Spanish, I didn't stutter much at all. I think that's because I was really focusing more on learning properly and getting things right. As I got the hang of it, of course, I began to stutter in Spanish too. However, when I studied abroad in Spain as a student with upper-intermediate skill, I rarely stuttered. Again, I think this was because I was surrounded by Spaniards and was very conscious of speaking the language correctly more than my stutter.