@Zedyeen, I think he is speaking about a future European Federation "United States of Europe".

But yeah, right now the language issue is only an inconvenience, it's not one of the bigger issues.
Technically you can live anywhere you want in the EU if you are a citizen, but practically it would be stupid to move somewhere where you don't know the language.

But having a language in common, which everybody felt comfortable about speaking, and which didn't hurt any national pride, or that wasn't hugely difficult to learn... .. that would definitely progress the EU project massively.

As it is now, there is a sort of "etiquette" about how and when to speak what language, what to do if you absolutely don't speak a certain language at a certain time... etc. It works reasonably well, but of course, occassionally there are misunderstandings or people that take offense or get angry at others because of language issues. This "etiquette" works in Belarus to the extent that people appreciate that you are making an effort speaking the language, and they are very kind and helpful when they realise you are struggling. But they normally do not attempt to try any other language, which is what normally would happen in the EU.

Occassionally it happens, in the EU that you are simply not able to make yourself understood - for example it happened recently to me in Romania and it happens a fair bit in the larger EU countries, or when people visit foreign countries as tourists and end up "off the beaten track".

In business situations it can be awkward because one party has a language advantage over another, and those who are forced to speak a language they feel uncomfortable in, don't like it. On the other hand, knowing a particular language can mean you get offered a job almost solely on that merit. This happened to me in England, and I have met 2 people who got really good IT jobs in Sweden, largely (I think) because they could speak Russian and the other applicants couldn't.