European Commission President Jean-Claude Juncker addressed EU lawmakers in French and German on Tuesday, in a shift from his usual style of also giving a portion of his speech in English.
The move was interpreted by many as a direct reaction to last week's British decision to leave the EU.
The European Union has 24 official languages, but the three main working languages are English, French and German. Britain's decision to split from the bloc has led to speculation that it could lead to a relegation of English, which is also an official language of Ireland and Malta.
Juncker only used English once during his 15-minute address to the European Parliament, to respond to a heckle from EU lawmaker Nigel Farage, the UK Independence Party leader and a key British Leave campaigner.
"To some extent I'm really surprised that you are here. You were fighting for the exit, the British people voted in favour of the exit, why are you here?" Juncker asked Farage.