I don't think it would be smart to let English be the only EU language. Will only make sure that even more people are pissed off by or uninterested in the EU. National governments, parliaments and their regional and local counterparts (yes, EU decisions concern them all) need to understand what comes out of Brussels as well. Besides, not even federal states in which people that speak the same language are regionally concentrated (Belgium, Switzerland, etc.) work that way. Why would the EU, a far less integrated entity?