Some general information on the use of induction motors.
1)60Hz fan on 50Hz grid: The fan you use is an induction motor, meaning that it will spin a bit slower, theoretically at 50/60 = 83% of its original speed. That's most of the time not a problem except that you feel a bit warmer :). However, induction motors are inductive loads and therefore draw more current on a lower line frequency, again theoretically 60/50 = 1,2 or 20% more. This is generally speaking not a problem.
2) 50Hz fan on 60Hz grid: The reverse happens.
3)Lowering the voltage of an induction motor does not necessarily lower the drawn current like in case of an electric heater. Depending on the type of load, amount of drop, motor design, a motor can experience more slip which actually makes the current increase @ lower voltage.
4)Lowering the voltage on an induction motor lowers the speed only in a controllable manner in case of a quadratic load. Coincidently, a fan is a quadratic load.
This behaviour is reflected in the datasheet. You nevertheless might want to take this into consideration in case the datasheet does not specify the above.