Bicycles are made so that when making a turn signal, one can brake on the hand not occupied making the turn signal with the primary brake, BUT with incorrect assumption what the primary brake is.
The incorrect assumption is that the primary brake is the rear brake. Thus on the right driving countries, the rear brake is on the right (because you make left-turn signal in these countries so the right hand is free), and on the left driving countries, the rear brake is on the left (because you make a right-turn signal in these countries).
My opinion is that this doesn't matter much for one-handed braking. Braking one handed either brake will do, as you can't brake hard with only one brake on the handlebars. Braking two handed, you probably want to use the primary front brake with your primary hand. Most of us are right-handed so that means the front brake should be on the right.
So, the safest option (assuming you are right handed) is to ensure your right brake is the front brake and use that setup always no matter where you ride the bike. On most of the countries, this means the brakes should be reversed.
There may be legal requirements for the default configuration of new bicycles sold, but a friendly bicycle shop will reverse the brakes on request, and you can always do whatever you want with your bike. Nobody is going to arrest you if you have two working brakes in the reverse configuration.
Note that some brakes such as V brakes have different parts for right-front and left-front setups. The right-front V brake has 135 degree noodle and the left-front V brake has 90 degree noodle. The 135 degree noodle allows for a slightly better cable setup for the right-front configuration, but this actually doesn't matter. A long time ago, I set up a V brake bicycle to have the right-front brake lever configuration, and the 90 degree noodle worked just perfectly.