The distant moon Pandora from James Cameron’s Avatar films is a feast of sci-fi world-building. Dragonlike creatures prowl the skies. Supersmart whalelike beasts write poetry under the sea. And a splendid variety of jungle plants glows multicolor in the dark. Cameronʼs famously stunning visual effects can make these ecosystems appear vivid enough to touch. But perhaps the most realistic feature of life on Pandora requires no high-tech cameras nor special effects to render: The language spoken by its native Na’vi people, though invented for the Avatar franchise, is very real. Some Avatar fans have even learned to speak it. The mastermind behind this made-up tongue is Paul Frommer. As a linguist at the University of Southern California in Los Angeles, he’s fascinated by the structure of languages. So when Frommer heard that Cameron was looking for someone to build a language for the first Avatar film, he jumped at the chance.…