i think two rear fog lights is misleading because it looks like brake lights. that being said... most, if not all British cars have two rear fog lamps, and newer German cars (eg. audi a6) and even one American car (Oldsmobile) has two rear fog lamps.

the general rule is whichever side of your car is closer to the center median, thats the side that the rear fog lamp should be on.

UK Crossfires have the rear fog lamp on the right side; German, Aussie, and probably others have theirs on the left-hand side of the car.