This classmate, first of all, give you a reassurance. English defense sounds very professional, but it has actually been formalized at present, which means that ordinary students can pass it smoothly without being nervous.

Since you are an applied English major, you must reply in English. I don't know if you are defending according to your paper. If so, the most important thing is of course your understanding of your paper, including the central idea, abstract and detailed arguments, which should be memorized. The teacher must ask questions around your paper during the defense.

For the sake of safety, you should defend according to the teacher's instructions. Don't argue with the teacher. One of our classmates failed because of quarreling with the teacher.

Good luck.