A GPS tracker that uses a SIM card works throughout the world as long as the SIM card works.
For a GPS tracker to operate it needs a Satellite signal and a GSM signal. The GSM signal is dependent on the provider associated with the SIM card in the tracker. Ensure you contact your SIM provider before going abroad to make sure it is data enabled for the country you are visiting.
Satellite coverage is sufficient in most cases outdoors regardless of the country you visit. However the satellite signal will be attenuated while indoors. If you are near a window or if there is a light roof overhead you may receive a signal.