It really depends. I personally took 3 days prior to the exam to study. This is only because I had just finished my internal medicine rotation, so interviewing patients and conducting physicals were already comfortable to me. I read over FA and had a friend act as a patient on a few cases. I took it in March, and I found out last week that I passed. I had either asterisks or above average performances, with nothing on borderline.
On the other hand, my classmate studied with 2 other students over skype for 3 weeks, and one of them did not pass. I did not ask for specifics pertaining to the failure, but it must have been a glaring mistake.
Spend as much time as you deem necessary. And yes... speaking English does help a lot. I've met some very smart students, but their English can definitely be an obstacle. Good luck guys