one, You didn't see the BMW after the incident, and did the police see the bmw?
two, produce proof that the scratch on your car occured prior to the incident
three, make sure you get a translator from the court and you ask to question the witnesses during the trial
four, remain calm
get a court date for now, do it asap, and postpone it once if it's possible, the chance are you will never go to trial with a small offence like this