Translation agencies are regularly involved in the translation between multiple natural languages, such as English to French, or German to Japanese. Human languages are often referred to as natural languages, and there are hundreds of different languages used around the world
However, for a translation agency (Übersetzungsbüro) , it is important to be able to deal with the most popular of these languages, in order to translate documents from one language to another. The most common languages in the world are English, Spanish, French, German, Arabic, Russian, Portuguese, Standard Chinese, and Hindustani. However, many translation agencies will specialise in a few of these languages, depending on their sphere of activity and their location.

English has become the global default language for international business and politics, and is vital for many international translation tasks. For example, a company in the United States may wish to translate product information and safety documentation into a number of European languages, or a French company may wish to translate communications into English in order to create a dialogue with an English colleague. Many translation agencies around the world specialise in a particular language or group of languages, such as the popular European languages or those from the Iberian peninsula.

In strict terms, standard Chinese is not recognised as a true world language, due to very few speakers outside of mainland China. Using this description, the biggest world language is English, with about 328 million native speakers and 1800 total speakers. Many sources have the Spanish language, or Castilian, at even more native speakers at between 330 to 400 million, although the number of total speakers are much smaller at about 500 million. All large international translation agencies need to work with English and Spanish, with many also diversifying into the most popular European and Asian tongues.