There are many many factors that can make stuttering better or worse in one language or another. For example, many people who stutter speak more quickly (it's like the mouth muscles can't keep up with the rapid flow of words from the mind). When speaking a second language, which is usually less fluent than the first language, it sometimes forces people to slow down their speech since formulating sentences in the mind takes more time, which can reduce stuttering. Another thing is that stuttering itself can increase the frequency of stuttering. For example, if you stuttered on the word "smile", the next time you go to say that word, you might be anticipating that you'll stutter on that word again. Anticipating/worrying about an upcoming stuttering event can actually make it more likely to happen and more severe when it does happen. In a second language, there may have been less of these negative experiences and therefore, you might not be anticipating a stutter as often. Even just believing that you stutter less in a certain language will likely make you stutter less. There are many many more factors that come into play. Source: I'm a speech therapist