The European Commission employs about 36,000 people, who may speak any of the EU's 24 official languages. In practice, to facilitate working together and a better understanding of each other, we mainly use three languages: English, French and German. Work within the Commission is usually carried out in one of these three.
Practically speaking, you will often hear a mixture of English, French and German during internal meetings. People will express themselves in the language in which they feel most comfortable communicating.
Information produced by the Commission (or meetings involving people from different countries) may require translation or interpretation into a number of languages. This is essential so that European citizens can have access to information about the EU in a language they understand.
Some figures to give you an idea: