They'd make an odd dinner party: The 12th century polymath Saint Hildegard of Bingen; James Doohan (aka Scotty from Star Trek); an American sociologist named James Cooke Brown; J.R.R. Tolkien; Gottfried Wilhelm Leibniz, inventor of the calculus; the feminist science-fiction author Suzette Haden Elgin; Anthony Burgess; and an assortment of 19th century characters (Martin Schleyer, Catholic priest; Jean-Francois Sudre, musician; Ludovic Zamenhof, ophthalmologist). Oh, and James Cameron.
What would they talk about? More importantly, what would they talk with? Their options would be rich, as all of these people are conlangers--creators of "constructed languages" like Doohan's Klingon, Zamenhof's Esperanto, Brown's Loglan and now, Na'vi, the language of Pandora (here's a phrasebook, in pdf form). (Credit where it's due: Doohan and Cameron supplied some sounds for Klingon and Na'vi, but those languages feel real because they were built by professional linguists--Marc Okrand for Klingon and Paul Frommer for Na'vi.)
Throughout history conlangs have been created by idealists, whose motives have fallen into a few general categories. Some sought world peace through better communication (via, say, Esperanto, or Sudre's solresol, a language made exclusively of musical pitches). Others aimed to make faulty thought impossible (via a purely logical grammar, like Leibniz's). Then there were the social activists like Elgin, who gave her laadan a comically anti-male semantics, with words for concepts men supposedly never think of, like, "to refuse to ask a question even though you know the other person wants you to."
Finally, there were writers who reveled in the intricate pleasure of pure art, fabricating a whole literature for the same reasons they invented convincing characters. That urge led Tolkien to invent Elvish, and Burgess to create a proto-proto Indo-European for Quest for Fire. Like beloved characters from novels who feel real, these languages often find a home in hearts and minds. People study Elvish, for example, and someone apparently has tried to raise his kid bilingually, in English and Klingon.
Now, we're seeing a new species of artificial tongue: One that is created as part of an entertainment franchise. In these cases, the arty-geeky appeal of fictional syntax gets supercharged by blanket marketing. A whole American childhood may pass without news of Esperanto, but everyone's heard of Klingon. Now, Na'vi looks to follow a similar path. They're both corporate conlangs.
Corporate sponsorship reaches the masses, but it has its drawbacks: over time, languages grow and change--they want to be free. That's not consistent with trademark and copyright protection. Esperanto can evolve, as its speakers decide what is and is not correct (though it is not a peaceful process). But Paramount could shut down the Klingon Language Institute tomorrow, or, worse yet, upend the language (maybe turn it into laadan?) to appeal to a different demographic.
A normal language is owned, for better or worse, by the people who speak it (at least it is after the Founder dies). A corporate conlang is owned by suits. Na'vi enthusiasts already feel the pinch, hence this online petition to Fox to "free the language." Corporate oversight endures, though, unless and until people speak a conlang in such large numbers that control-by-attorney becomes impossible. Wouldn't it be cool, if Na'vi takes off, if one day its speakers end up driving out the Sky People and liberating their tongues?