On 1 February 1946, the 21st Plenary Meeting of the United Nations General Assembly adopted a resolution approving the rules of procedure concerning languages.
“1. In all the organs of the United Nations, other than the International Court of justice, Chinese, French, English, Russian, and Spanish shall be the official languages, and English and French the working languages.
2. Speeches made in either of the working languages shall be interpreted into the other working language.
3. Speeches made in any of the other three official languages shall be interpreted into both working languages”.
The verbatim records of General Assembly meetings were conducted in the two working languages. However, they could be translated into any of the official languages at the request of delegates. All important documents, including resolutions, were reproduced in all of the official languages.
The General Assembly planned to install a system of telephonic instantaneous interpretation that would dispense with the consecutive interpretation system, which was more time-consuming and costly.
The languages approved in 1946 are still the official languages of the United Nations. In 1973, Arabic was adopted as an official UN language.
Sources:
‘Interpreters At The United Nations: A History’ by Jesús Baigorri Jalón
Inclusion of Arabic among the official and the working languages of the General Assembly and its Main Committees, Resolution 3190 (XXVIII) adopted on 18 December 1973, A_RES_3190 (XXVIII)
UN General Assembly, Rules of Procedure Concerning Languages, 1 February 1946, A/RES/2
UN General Assembly, Simultaneous Interpretation System, 7 December 1946, A/RES/75(I)