I live near Montreal and regularly flew in its airspace for years. It’s not required. Many, self included, would do so as a courtesy, but many Quebec pilots are unilingual and unable to communicate effectively in English; I would regularly hear both languages used in Montreal controlled airspace when flying in it. Transport Canada regulations require only that a pilot can speak English or French. Of course if the latter, you’re pretty much limited to flying in Quebec, and Ottawa only.
602.134 (1) Any person operating an aircraft who wishes to receive the services referred to in this section in one of either English or French shall so indicate to the appropriate air traffic control unit or flight service station by means of an initial radiocommunication in English or French, as appropriate.
ICAO only requires language proficiency in English, or the language understood by the station on the ground, in the case of Quebec, and Ottawa, that language is French, in addition to English. That applies to pilots. controllers handling international traffic must be proficient in English:
In which languages does a licence holder need to demonstrate proficiency?
Amendment 164 to Annex 1 has introduced strengthened language proficiency requirements for flight crew members and air traffic controllers. The language proficiency requirements apply to any language used for radiotelephony communications in international operations. Therefore, pilots on international flights shall demonstrate language proficiency in either English or the language used by the station on the ground. Controllers working on stations serving designated airports and routes used by international air services shall demonstrate language proficiency in English as well as in any other language(s) used by the station on the ground.
So even in aviation, which does have an “equivalent” to Latin, the “vernacular” (local language) is allowed for local pilots.
Similarly, the Church allows the vernacular, so her Gospel message and the Graces it confers is understood by all!