I know that flight simulators (which are used to train the pilots for commercial airlines) try to simulate almost all kind of weather conditions, but how effectively and realistically are they able to reproduce turbulence in the simulated environment?
No, simulators cannot realistically simulate turbulence. Turbulence is characterized by significant changes in altitude that happen very quickly, and even full motion simulators aren't going to be able to re-create that. They can bump you around a bit, but not really prepare you for the real thing.
It depends what you consider realistic. A full motion simulator can slam you around pretty fearsomely, but there is always the limited travel of the motion actuators to consider of course. As opposed to the real world where the amplitude is infinite.
Simulators can realistically simulate turbulence, as in a vibrating aircraft. Modern Level D simulators on electrical motion systems can reproduce vibrations between 0 - 20 Hz at a teeth rattling amplitude. They can also produce downward accelerations at over 1g, making the occupants being ejected upwards from their seats. This can be used to simulate high altitude wind shear effects, while making the altimeters tumble.
Motion systems can bump you around a lot. I'm not sure what the training value of slammin a flight crew through full turbulence would be though - would they pick up any extra skills that could prevent an accident?