Some of this can be explained by looking at the evolution of brakes. If you have a single brake lever, it usually is placed on the right (most people are right-handed).
With coaster brakes, you use a single brake lever to control the front rim brake. It makes sense to put this on the right. So in countries where coaster brakes were prevalent, the front brake is controlled by the right hand.
These countries include Germany and Britain.
That much makes sense. (Note that Germans drive on the right, Brits on the left, so the "turning across traffic argument" does not hold much water for the Germans.)
Countries that used rim brakes from the beginning often used the opposite "left front" approach. France is the best example. Maybe because they started with rear brakes only, once again putting the single brake lever on the right? I really don't know.
Personally, I prefer the "left-front" approach. The reason is simple: I often eat while riding, and being right-handed, I use my right hand to rifle through the handlebar bag or hold my food. But I need to be able to brake while doing this, and since I use my front brake predominantly, it makes sense to use the available left hand to activate it. -- Jan Heine, Seattle Editor/Publisher Vintage Bicycle Quarterly c/o Il Vecchio Bicycles 140 Lakeside Ave, Ste. C Seattle WA 98122 http://www.vintagebicyclepress.com