Based on Annex 1 to the Convention on International Civil Aviation (eleventh edition, July 2011), Chapter 1, Paragraph 1.2.9, "Language Proficiency", sub-para. 1.2.9.1, he was quite categoric that pilots who use FR-only aerodromes flying on a non-French licence must have proof of French language proficiency (Level 4 minimum) entered on their licence.
Fortunately Annex 1 is not Law so under what European legislation do they justify this comment?