Leo, I googled "ICAO" and found the Chicago Convention of 1948. It contains the following bit...
PART IV. FINAL. PROVISIONS
Paris and
Habana
Conventions
CHAPTER XVII
OTHER AERONAUTICAL AGREEMENTS AND ARRANGEMENTS
Article 80
Each contracting State undertakes, immediately
upon the coming into force of this Convention, to give
notice of denunciation of the Convention relating to
the Regulation of Aerial Navigation signed at Paris on
October 13, 1919 or the Convention on Commercial Avia-
tion signed at Habana on February 20, 1928, if it is
a party to either. As between contracting States, this
Convention supersedes the Conventions of Paris and
Habana previously referred to.
I have to go to bed now or she'll get the hump as she has to get up early but it might just be worth doing a search for the Regulation of Aerial Navigation 1919 or the Convention on Commercial Aviation 1928. I bet it's in one of those.
Anecdotally, I have been led to believe that English was adopted over French by just one vote. Seems likely with all the French-based words in common usage (M'aidez, etc.).
Hope it helps.
Link to ICAO page with Chicago Convention