At the point of early 1946, it should be noted that Chinese, French, English, Russian and Spanish were chosen as official languages - the fact that the General Assembly's second ever resolution (in its first ever session) was concerned with language use should point to the importance of establishing a working language, sandwiched between establishing a "Commission to Deal with the Problems Raised by the Discovery of Atomic Energy", and how to deal with war criminals. (French and English were the working languages, joined only by Spanish in 1948). Only in 1980 would Arabic be added as both official and working language. The text of the 1946 resolution itself is fairly bland and doesn't give much hint of these debates, which in itself is not atypical for a UN resolution: however the minutes of this meeting right now are more telling.

The legal basis for multilingualism was to be found in the Charter: "the present Charter, of which the Chinese, French, Russian, and Spanish texts are equally authentic..." (emphasis mine). Even at the San Francisco Conference, the question of language use emerged. French and English dominated at interwar international organisations, but the Soviet Union, China, and Latin American countries (as the UN's official languages would eventually reflect) sought to change this. Latin America countries had a significant presence at San Francisco, representing a third of those in attendance. Jesús Baigorri Jalón's "Interpreters at the United Nations. A history" discusses this, although there is a frustrating gloss over a significant categorization of languages - "Whatever the reasons, a compromise was reached whereby "official languages" were differentiated from "working conditions".

Nonetheless, there was significant anxiety from the French that the absence of their language at San Francisco (owing to Nazi occupation and De Gaulle's marginalisation at that point) would lead to French potentially losing its status as a diplomatic lingua franca, or at best serve as a distant second to English. Le Monde describes the first plenary meeting, where French was made equivalent to English after a lengthy debate. Notably, the Chinese delegate asserted that should English not serve as the only official language, then Chinese would have to be used; Honduras followed likewise with Spanish, as did Portugal. Some interesting rhetoric was used by the French delegate, who asked if the rest, "like Hitler... too wanted to condemn France". What Le Monde leaves out is the support from the Chilean, Venezuelan and Peruvian delegate that French should be used, while the Chinese representative remained more skeptical but drew a distinction between 'official' and 'working' languages as a compromise should all negotiations be carried out in English.

French and English were made working languages, with explicit reference to the bilingual model of the Canadian Parliament, with the speeches translated into all 5 languages a day later (no comment is made as to whether this time lag was protested). The concern over preserving the status of the French language here is articulated in more desperate terms, a far cry from attempts to defend an existing monopoly of French in 1919. Jalón suggests that the status of French was quite precarious, barely maintaining its presence as a working language.

In 1946, a sub-committee would be created to interpret the status of this multilingualism, comprising the UN Committee President, Vice-President and Rapporteur, and representatives from Brazil, Canada, China, Czechoslovakia, Egypt, France, Mexico, the Netherlands, Norway, the Soviet Union, the UK, and USA. Some members, noting that half of the committee did not have their native languages represented, suggested that only one or two working languages could be used- just like how diplomacy was expedited in the Middle Ages!

Ultimately the representatives were also concerned not just with what language to use, but the practical process of communication, which involved a debate over interpretation- should it have been simultaneous (which ran the risk of being imprecise) or consecutive? It should be noted that Jalón himself relies a lot on Ostrower's account (published 1965) of the conference and international language use. To my knowledge not much has been written on this matter, but I suspect that going through archives and correspondents of attending representatives might yield something. I've previously skimmed through the UN Career Records Project (deposited) at Oxford's Weston Library, but not much of this stood out to me amongst the British diplomats and administrators I examined.