Why should Europe adopt English as its prime language, seeing as it's a MINORITY first language!
If we're going to adopt "a european language" I would much rather adopt that OTHER international language, which also happens to be the most widely spoken first language in Europe! Any ideas which one?
Actually, it's a language group, rather than a language, but it's Romance, or as we could call it "modern latin". When you add together all those people whose native language is a derivative of latin, it is the most common language, outnumbering the germanic languages combined, or the slav languages combined.
As for English, Finnish, Hungarian, (French?) they hardly register!
My personal preference, actually, would be to select those major language groups (English, French, Germanic, Romance, Slav) and say that all official texts must be in one language from each group. It is up to the proposer to provide those official translations, and then every country can translate into their own specific language. And if there is a dispute as to meaning, the country that provided the original document has to use the translation, not the original! (For other disputes, the original would trump.)
Oh - by the way - I am a native Brit who's only Romance language is school latin (though I do speak German, French and Russian).