Hey! I'm a speech therapist and I stutter too. I can try to shed some light on this, but the research is still ongoing. I'll give you the simple explanation and the more science-y one: People who stutter are often more fluent in their second language because of the preciseness and amount of cognitive effort it takes to speak the second language. However, when a person becomes more “fluent” in their second language and spend less cognitive effort on preciseness, their stuttering can emerge in the new language. This is a bit like letting our guard down. It sounds like this is what is happening for you. To get really in depth, there is a theory that stuttering is caused by a misallocation of attention, i.e., of perceptual- and processing capacity during speech. The causal chain is: Symptoms are a brain response to invalid error signals in the monitoring system. The invalid error signals result from a mismatch between expectation and feedback. The mismatch is caused by auditory feedback disruptions due to insufficient capacity for feedback processing because of the misallocation of attention. There's a bunch of jargon in that description, but it basically boils down to an issue with our self-monitoring system while we are talking. Given that theory, it does make sense that if you are attending more to what you're saying and how you are saying it when learning a second language, you would stutter less. There is still more research to be done and other theories, but this is a big one. In my experience learning second languages, I stutter about as much as in English (my first language), so experiences will be different for others. Every brain is a little different!