Adding an additional fan will not solve your problem. Fans are only good for up to about 40 mph [~65 kmh]. Anything beyond that speed, the incoming rush of air is more than what the fans can push/pull.
That said, the environment conditions in Japan will have no affect of how your car is built. They are all built to operate in a variety of climate conditions from freezing to extreme heat. All cars are made to be able to handle the temperature variances. Further, Sri Lanka is not that much hotter than Japan during summer.
I think your best bet is to root cause the issue and address it rather than adding a fan. First and foremost, make sure the obvious things are not malfunctioning. i.e. temp gauge, thermostat, water pump in good condition with no damage to the bearing, clogged radiator fins etc... Your problem most likely is caused by water flow problem. Also inspect the radiator fins from the outside and make sure that they are not overly bent or clogged with foreign debris blocking the air from passing through the radiator.
Good luck.