WHBM, It is simply not legal to fly an N registered aircraft on an International route without having an FAA licence or at least an FAA foreign licence validation.
In more modern times, the requirement is that if the a pilot is domiciled within the EU and is flying an N registered aircraft within the EU, then that pilot is required to have the equivalent EASA licence and rating.
The days of dual licensing and dual ratings are upon us, and actually have been for some time.