The Importance of a Common Language in D&D

The most obvious one for that, and the one that like if I'm building a D&D world, I would probably want to change is the whole thing of one language per race. Do you mess with those relationships much or? Not as much as I want to. And I think that's a matter of time. The reason that you probably have one race for one language in all of the D&D settings is because they're all rather self-contained.