You may be surprised, but it is your English! Almost all interviews start with a phone call. Your English is what leaves the hiring manager the first impression, which can decide if s/he is interested in asking you more in-depth questions. Clear pronunciation and correct grammar give you an advantage over other candidates who cannot do this. If you have limited time before an interview and you want to improve your odds of getting the job, I would suggest you put a big effort into improving your English.
The question is how. It may not be as hard as you thought. I think most foreign students particularly the Chinese students have a good English foundation. What makes them rusty in English is that they spend too much time speaking their native languages. I know some Chinese students who live with Chinese roommates, watch Chinese TV and chat online using Chinese. How can they expect to speak fluent English! Studies after studies have shown that the biggest obstacle for someone to master another language is frequent switching back to their native languages. For example, after a period of intensive immersive training on a foreign language, a student had shown remarkable progress in the foreign language. His/her language fluency would drop noticeably for a couple of days if this student received a letter in the native language or met a friend with whom he/she spoke their native language for a couple of hours. The upside of the study is that one can quickly become more fluent in a foreign language if one is immersed in it for a few days. In this case, one’s brain will switch to a mode of speaking that language.
To increase your odds to get the job, the obvious strategy for a candidate whose English is less than ideal is to immerse oneself in English until the job interview. Stop watching TV or chatting online in your native language. Make a deal with your friend to speak English. Watch English news programs or even some sitcoms that you love in English. Of course, practice interview questions and answers till you can answer the questions without sounding like you memorized them. Remember you don’t have to be perfect, you just need to be at your best! That is all you can ask yourself to do.
For new students just come to the U.S., I would suggest you put speaking fluent English as the #1 skill you want to acquire coming to study in the U.S. Try to find a non-native language speaking roommate. Avoid watching TV or chat online using native languages. Think about it. You can learn math, computer science, mechanics, engineering probably equally well at a university back in your native country. Studying here offers you the opportunity to practice English every day. It is a missed opportunity if you don’t take advantage of it.