I agree with everyone that deferments are granted on a case-by-case basis, dependent on the school.
However, the time before medical school will the the last time in your life that you are able to take time off for an extended period of time. After school starts, you get a couple summers off and that is it. If you think an international rotation during school would satisfy what you want to do, then you might as well start school now. If you're planning on being international for more than a couple months or if you are going to multiple places or if you want to do non-medical related things there, then pitch your case to the school and live your life how you want to.
I'm a big advocate for time off between undergrad and med school to do things for yourself. Starting school 1 year later isn't going to matter a bit in the long run.
Good luck-