don't stuttering when speaking other languages ????

don't stuttering when speaking other languages ???? so guys i have a very very light stuttering problem in real life,and well this affects my life somewhat. and a very funny thing is that i stutter when speaking Portuguese (PT-BR) but i NEVER stutter when speaking english,NEVER. I get really nervous when i have to read some Pages from the School book to my colleagues,my heartbeat goes CRAZY,and some days i don't stutter,other days i don't. but...when it's english class,i'm like a U.S native. What the fuck ????