Hi Pieter,
This International Driving Liscence is a bit of a strange thing.
I remember, many years ago, my father aplied for one from the ANWB (Dutch car owners organisation). I can't recall for what country exactly. But I heard it's actually more something of a "money maker thing" then that it is a real requirement.
When I rented a car in South Africa my Dutch liscence sufficed.
Cheers,
Roy