The official languages of the EU institutions are every one of the 20 official languages. However, in practice, not every institution works in every language. Only the European Parliament, the Council of the European Union, the Economic and Social Committee and the Committee of the Regions use every official language of the EU. Working languages of the Commission are English, French and German. The working language of the Court of Justice is French. The working languages of the Court of Auditors are English, French and German. The working language of the European Central Bank is English.
In the weekly meetings of the commissioners, English, French and German are typically the most used languages, but in theory, the commissioners can use their own language (which some indeed do from time to time). Within the administration, the languages are usually limited to English and French.