Okay, so recently as I was coming down the stairs in the dark and trying not to fall and break something I had the random thought that if I had to pick a real world language as the "common" for a game world (for place names, personal names, terms for things, etc.) it would be French. But that got me wondering, after I made it safely down and over to the refrigerator to forage for a snack, that maybe using real-world languages for the peoples of a fantasy RPG world is a cop-out.
One of the things that made the Lord of the Rings so engaging and immersive was the use of carefully constructed fantasy languages (okay, so the Riders of Rohan were very Anglo-Saxonish). It really gave the setting a cool yet realistic feel. By comparison a lot of fantasy settings use lame random names which don't hang together linguistically. (As an aside, one of my major pet peeves is GMs and players using lame names for characters. I want a certain level of immersion and names like "Bobby-Ray the Stupid" totally trash any suspension of disbelief. If you suck at coming up with names there are web sites with lists and random generators--find one and use it!)
An easy way to get linguistic coherence is to borrow real-world languages for particular regions or cultures in a campaign world. One good example of this is the world of Warhammer Fantasy. The Empire draws on German, Brettonia draws on French, etc. However, using real world languages tends to channel people's thinking into including historical and cultural stereotypes with the language. That may be exactly the effect you're looking for, as in Warhammer Fantasy, but it may not.
Anyway, I've always liked the sound of French and placenames in France. It would be my go-to language for a quick off-the shelf real world language. And so if I needed a quick off-the-shelf campaign map I could just grab the one for Brettonia.
So, what do you think? Is using real world languages dorky or dynamite? And what would be your first choice of language?