I am currently reading A World Lit Only By Fire by William Manchester. In his discussion of the early days of the printed word, he brings up the fact that, if you wanted your book to be widely read, you wrote it in Latin. The educated peoples of most European countries at the time knew Latin, whereas the learning of the languages of other countries was far less common. Latin used to tie Europe together, at least, linguistically.
In most of my campaigns, I usually set Common up as the language of a fallen empire, sometimes one from distant antiquity, sometimes one that was recent history.
In my present AD&D game, there is no Common language.
Just some food for thought.