You will always stutter more in a language that you are not fluent with. With the languages you use daily, you dont have to search for words in your mind. mind processes the words faster. With other languages, your mind will always "search for" words while processing the thought and this causes the trigger for the stutter. I know 4 languages (hindi, english, bengali, punjabi) but i always try to stick to my mother tongue hindi or english (business language)