A working language (also procedural language) is a language that is given a unique legal status in a supranational company, society, state or other body or organization as its primary means of communication. It is primarily the language of the daily correspondence and conversation, since the organization usually has members with various differing language backgrounds.
Most international organizations have working languages for their bodies. For a given organization, a working language may or may not also be an official language.
UN Working Languages 
Originally English and French were established as working languages at the UN. Later, Arabic, Chinese, Russian and Spanish were added as working languages in the General Assembly and in the Economic and Social Council. Arabic, Chinese, English, French, Russian and Spanish are the working languages of the Security Council. 
Examples of common International organizations 
English and French 
The International Criminal Court, have two working languages: English and French; all Secretaries-General of the UN, therefore, are required (unofficially) to be fluent in both. The Council of Europe and NATO also have English and French as their two working languages.
Other groups with one or two working languages 
- The Arctic Council Indigenous Peoples Secretariat has English as its sole working language, though communications are also published in Russian. Although many circumpolar indigenous people speak either an Inuit dialect, a variety of Saami or a Ural-Altaic language, English is likely to be the second or third language that many of them will have in common.
- The Shanghai Cooperation Organization has two working languages: Chinese and Russian.
- Mercosur has two working languages: Portuguese and Spanish.
- The government of East Timor has Indonesian and English as working languages alongside its official languages (Tetun and Portuguese) and 15 other recognized local languages
- The state of Goa in India has Marathi as its working language. but only Konkani has official status in the state.
English, French and Spanish 
The World Trade Organization, the International Telecommunications Union, the International Labour Organization, NAFTA and the Free Trade Area of the Americas all have three working languages: English, French and Spanish.
Other groups with three or more working languages 
- The European Commission has three working languages: English, French and German.
- FIFA has four working languages: English, French, German and Spanish. Formerly, French was the organization's sole official language. Currently, English is the official language for minutes, correspondence and announcements.
- The African Union currently uses Arabic, English, French, Portuguese, Spanish and Swahili.
- The Southern African Development Community has four working languages: Afrikaans, English, French and Portuguese.