How to prepare for an interview when you are in between jobs?

I have an over-the-phone job interview with the UN but it's kind of a bad timing?

• I am a teaching assistant and has 64 undergrad papers to grade for the same day as the interview. I can't postpone the interview nor can I key in my grades at another moment. It's for an internship and I'm wondering if 5hr would be enough to prepare for the interview? I can't pull all-nighters anymore, my body tends to need its beauty sleep lately. I'm very nervous since English isn't my mother tongue and I tend to practically screw up during jobs interviews conducted in English, especially when I am nervous. This time, I can't help but thinking "It's the UN for crying out loud! This opportunity won't come around twice so you have to be perfect." If anyone has ever worked for them, could you please tell me how fluent in other languages are the English-speaking people? I mean, do they speak French, Spanish, Arabic or Russian as well as they master English? Thanks for your answers.

• Answer:

  It is all down to how badly you want the job, study every waking hour and good luck.