My mother tongue is Cantonese but I grew up speaking English. I tend to stutter a lot more in Cantonese than I do English, but I suspect that part of the reason why is because I'm not as fluent and it's much harder for me to employ my usual strategies/workarounds. With English it's much easier for me to quickly rephrase something or substitute words because I have that vocabulary. I'm also learning Mandarin at uni and it's somewhere between Cantonese and English in terms of my stuttering. I get blocks on a lot of the same sort of consonants (like 's, f, ch) in both Mandarin and English.