A common statement, spoken by musicians who love to think about what they do, is that music is the most common language. No matter where you go, if two people can read sheet music, they can play music together. Perhaps this is a good argument for learning how to read music after all! Being literate can't be a bad thing. It can't be bad to be able to communicate with others, but the same could be said about guitar.
There is a common language spoken between most guitarists. It's a simple one that we can use to skirt past language difficulties. Pop songs are popular by definition. If two radically different persons both played guitar, chances are they will be able to communicate if they know the same song. If by chance these two people knew how to play the chords D, G, and A on the guitar, they could both play Twist and Shout by The Beatles. Or Dead Flowers by The Rolling Stones. Or Turn it On by The Flaming Lips. The list goes on.
Maybe it's just me: Fluency in all the languages of music is nice, but I dig guitar's vernacular the most.