Originally Posted by RoadWarriorFromLP

The authentication comes from the fact that an agency located in the country where the license was issued has confirmed that the driver has provided "proof of his competence" to drive, as is required by the treaty. (For example, AAA does this for IDPs issued in the US.) Instead of taking a driving test every time you cross a border, foreign nations that signed the agreement will rely upon your home country to vouch for your driving ability.

The treaty provides all of the participating nations with the option to require an IDP, but also provides two underlying motivations for doing so: (1) some nations didn't issue driver licenses at the time and (2) licenses generally did not follow the model license format outlined in the treaty, which basically called for a booklet format that included your birthplace and a photo, presumably similar to a passport. Translation wasn't the issue.

Originally Posted by lansbury

Thanks for teaching your grandmother to suck eggs. I only dealt with the things for 30 odd years and know exactly what they are, how they are issued and the worth of the paper they are printed on. They translate a driving license from one language to another, no more no less.

Even AAA say this about them "It translates your identification information into 10 languages — so it speaks the language even if you don't"

Originally Posted by MidAtlantic

Does it matter? Maybe it does both. It obviously provides a translation and, insofar as the issuing body has to check the national license that you have, it authenticates it.