I would suggest that you pick the language that you and the interviewer are both the most comfortable that doesn't make you look like an idiot because you barel

I would suggest that you pick the language that you and the interviewer are both the most comfortable that doesn't make you look like an idiot because you barely know it. So for instance if you know java/c++/javascript and the interviewer is a Java coder, go with java. Don't pick some language you are messing around with on the weekend. It may be a bit counter-intuitive but the person doing the interview can have about as much mental overhead as you while solving the problem. They are likely writing down the answer you are giving and their thoughts on how you are doing. They also have to see where they think you are going to make a mistake and decide if/how to guide you to keep you on track. They also have to handle different styles of answering the question and have to know very quickly if it will work. So using a language they are comfortable with makes it easier on them and since in then end the job comes down to how they "feel" about your performance, making them feel better during the interview is going to help. That said I did do an interview for a gaming company in ruby because I didn't want to embarrass myself in c++ (which I barely knew at the time). They said after I took the job that it was hard to evaluate me because I was coding in ruby on the board and they were unfamilliar with it. Also I got several "You can do that in ruby?" questions. And one shake of the head when I defined a ease of use method on Hash on the fly to make the solution read nicer.