I haven't interviewed at Uni of Florida but I have interviewed at three schools so far and for each one of them, I went over the interview feedback page on SDN. That really helped me. I would suggest you to do the same.
English isn't my first language either so I understand your concerns. The thing to remember for applicants like us is to speak slowly and clearly otherwise we run the risk of rambling or going off on tangents.
UF is a great school. You got an invite, so you have already won more than half the battle. I don't think you have anything to worry about. Just be confident in your replies. Do not be self conscious. They understand most people are anxious before interviews. Good luck