Do people who are really nervous regularly fail polygraph tests?:
Polygraphs use a baseline and go from there. If your friend was nervous from the start then that would be his baseline. I measures changes not overalls. The would have to be extreme for him to fail. Even if his English was not par it shouldn't have any effect. I know you want to stand by your friend so do what you think is right. Have him volunteer for another poly from a different reader.