I gave lots of interviews and all of them in English ( since it is not my native language. I generally take lots of time to explain one simple and sort thing) and the main part where I am still stuck in my introduction. But there were 2 interviews where I already asked the interviewer in the beginning can i give my interview in my native languages and they allow. And those two are my best interviews and even interviews said i explained so many things that generally lots of candidates don't say. So, in short just ask the interviewer if he/she is allowed to give an interview in native language because it's reduced your stress so much and it's also possible the interviewer might not notice your strumming problem. Note: this is my experience Your might be different.