@Steve *******
that convention is superceded by the 1968 Vienna convention. Here's what it says on the language point so in strictly speaking an IDP is required. You've been doing well getting away with it for all these years
2. Contracting Parties shall recognize:
(a) Any domestic permit drawn up in their national language or in one of
their national languages, or, if not drawn up in such a language, accompanied by a
certified translation;
(b) Any domestic permit conforming to the provisions of Annex 6 to this
Convention; and
Annex 6 is mostly about the format of your license but states it must be in Latin or English script and MUST contain the words "permis du conduire" in French. Don't ask me why