Many agencies and institutes of European Union (in fact, all of them) use the English as the main official EU language. But, after the UK decision to leave European Union, there will be no other country with English as main official language. In Ireland, English is a secondary official language, after Irish and Ulster Scots, and in Malta is also a secondary language, after Maltese.
There are two solutions only to this problem: to remove English as official language of European Union, or to keep it.
If the English language will be removed from the official EU languages, there have to be changed ALL the documents (some of them are in English only).
If EU legislators try to keep it, there have to be found a very good reason. One reason can be that every member state is allowed to nominate as official language of EU one of its recognized national languages. So, Ireland or Malta can states English as his national language to be included in EU official languages. Many EU officials support the keeping of English as official language, without an official nomination from a member state.
If Ireland or Malta will propose English, that country has to change English as its main official English.
Anyway, the French people already enjoy on this issue: “Le français peut-être la langue de l’Europe?” (Could French be the Language of Europe?”) is the title of the talk of French Senator Jacques Legendre during the celebrations of the French Language in the world (La Francophonie dans le Monde).