English is my second language, and while I wouldn’t mind changing the official language of my country, I can’t see that ever happening, there’s just so much culture attached to the language, that would be forgotten together with our language.
On the other hand, economic suicide is assured by insisting on a high standard of living while doing everything possible to prevent innovation.
The same would happen if you managed to get the entire EU to agree to switch to one single language (remember, it's likely that it would be French or German instead of English). As a result of pushing adoption of the new first language, it would mean increased cultural output in that language, and a reduced output for the others. After a while, the differences will start showing.
I've lived in Denmark for quite a few years and I agree that people in Copenhagen and the other larger cities wouldn't notice that much of a difference to begin with, but remember that this would mean a cultural shift that will take multiple generations. Ask the German speakers in southern Jutland in another 24 years, and compare how their culture thrives compared to how they did before the war and you will probably have a pretty decent view on how the situation would be for many, many of EU's minorities 100 years after the switch to a single European first language.
Modern languages already have words for things like a mouse, a screen or the Big Bang, but it's all stupid stuff like an analogy to how a computer mouse looks like an animal because of its long cord-tail, a reference to the white screen a projector casts it's projection on, or a vulgar put-down of a theory being like God's orgasm.
If we take a dead language and start adding in vocabulary, we can quietly sweep that all under a rug before we encounter any alien species we have to explain ourselves to.
"You're the most pathetic people in the known universe."