We rented cars in Tahiti last year and neither an international drivers license nor any special insurance was required. Accept for the area around Papeete, there wasn't much traffic and the roads were two-lane, but good..
The only place to rent a car is Papeete, the capital of Tahiti. We did this for a day and it was lovely ... easy driving after you leave the city, very few cars and wonderful scenery. You won't need an international driver's license.