French President Jacques Chirac showed his temper at the EU summit when a French business leader addressed delegates in English.
President Chirac is a proud defender of his native language
He stormed out of a session when Ernest-Antoine Seilliere said he chose English "because that is the accepted business language of Europe today".
Mr Chirac told reporters on Friday he was "deeply shocked" that a Frenchman chose to address the summit in English.
Protectionism has emerged as a hot topic at the Brussels summit.
Mr Chirac's protest came when Mr Seilliere, the French president of the employers' association UNICE, said he would address the meeting in English.
According to a French official, Mr Seilliere was interrupted by Mr Chirac, who asked him in French why on earth he was speaking English.
He replied that English was the working language of that particular session and the accepted business language of Europe today.
Mr Chirac, Foreign Minister Philippe Douste-Blazy and Finance Minister Thierry Breton left the room.
Mr Chirac returned to hear the French president of the European Central Bank, Jean-Claude Trichet, address the leaders in French.
He later explained his actions, saying: "France has great respect for its language.
"It has been fighting for a long time to establish the presence of the French language - whether it be at the Olympic Games, where it was contested for a while, whether it be in the European Union, or at the United Nations."
He added: "Faced with the efforts that we are making constantly, particularly within the European Union... I must say that I was deeply shocked to see a Frenchman speak at the council in English. That is the reason why the French delegation and I left, rather than have to listen to that."
It is not the first time Mr Chirac has made a point of defending the French language in the international arena.
At previous gatherings he has stuck to French, using an interpreter to translate into English, despite the fact that he has a good understanding of English, having spent time in his youth as a Harvard student and forklift driver at a US brewery.
Mr Seilliere went on to urge EU leaders to "resist national protectionism in order to avoid a negative domino effect".
Italy has accused France of protectionism over a controversial deal to merge Gaz de France and Suez, which was a takeover target for Italian firm Enel.
Mr Chirac rejected the charges on Friday, telling reporters: "When I hear talk of French economic protectionism, for me that is complete nonsense".
French used to be the lingua franca for most EU business, but with the expansion of the EU to 25 member states, English is becoming even more dominant.
European Commission President Jose Manuel Barroso, who often switches between languages in speeches and press conferences, later stuck to French in his address to the meeting.