Can't vouch for truth, but if true, rather amazing. The question and answer are from Quora.
Why didn't the Latin language thrive and spread like the use of English today, given that it had the powerful backing of the Roman Empire?
I will tell you a little story. A little under a year ago I was on a business trip to Europe. In meeting in Italy there were six of us: two Italian speakers, two Portuguese speakers and two Spanish speakers. Can you guess the language we were using in the meeting? Are you sure? Well, you're wrong: each one of us used his mother tongue and we were perfectly able to understand each other, only having to explain a word every now and then.
The reason why this happened is because Italian, Spanish and Portuguese are in the end just different dialects of Latin. We call them languages because they're established as official languages of different nations*, but I'm sure a Roman legionnaire would find less differences between them than what were found in Latin as spoken in different parts of the Roman Empire back in the day.