"You speak Romulan, Cadet?"
"All three dialects, sir." –Lt. Uhura, Star Trek, 2009.
Somewhere out in space, in the Beta quadrant of the Star Trek Universe, there's a planet called Romulus. It's a planet a bit bigger than Earth, and has about 18 billion people on it. But Earth, with a third as many people, has about 7,105 languages, while Romulus has just "three major dialects."
In fact, as you look at language-users in science fiction, from the Kzinti of Larry Niven's Known Space to the bugs of Starship Troopers to all the aliens in Star Wars and beyond, though they may command a vast space-faring empire across many cubic light years of territory and billions if not billions of billions of sapient speaking beings, they never seem to command more than a handful of languages. By contrast, on our lone watery rock in a measly little corner of the galaxy, we Earthlings have thousands of languages with perhaps tens of thousands of dialects. Looks like sci-fi writers have really screwed up, huh?
Well, maybe. Or maybe not. There are two ways we can look at this one planet, one language problem. And they might just save the integrity of both science fiction and linguistics.
The first one has to do with a theory of "linguistic universals," or characteristics that all languages have in common. For example, all languages appear to have a distinction between noun-like things and verb-like things, different pronouns for 1st, 2nd, and 3rd person (we, you, they), and, for spoken languages, sounds that include both consonants and vowels. But why? Why should there be any similarities at all between the Dyirbal language spoken in Australia and the Basque language spoken in Europe on the other side of the globe?
Linguist Noam Chomsky believes these universals point to the fact that deep down, all human languages are fundamentally the same—that there exists in human brains one single Universal Grammar—and that every language spoken today evolved from the same great-great...great-grandmother tongue, the first language of homo sapiens. All the differences we think we hear between, say, English and Yupik, are really just minor surface variations on this Universal Grammar—little more than different dialects of a single "Earthan language". Chomsky has even argued that if a Martian linguist were to come to Earth, they'd conclude that all 6 billion of us speak just one language.) And so if a Romulan communications officer where fly past our planet, they would hear Japanese and Ojibwe like we hear British and American English.
From a strict Chomskyan perspective, then, there's absolutely nothing wrong with a human linguist describing the all the variations of language of all 18 billion speakers on Romulus as little more than "three major dialects" of a single language. No matter how vast their Star Empire may be, they'll all sound the same to us puny humans.
But then again, if we take Chomsky's ideas one step further, we may not even recognize Alien Language to begin with. Because aliens would have different brains, evolved under a different set of circumstances, Alien Language also would have a different set of underlying universal grammatical principles, unrelated to anything we've got in Human Earthan Language. We'd be lucky if we could even learn to say "hello" to these beings, let alone "take me to your leader".
But Chomsky's Universal Grammar isn't the only way of explaining linguistic universals. There's another group of researchers, represented by the linguistic anthropologists Charles Hockett and Terrence Deacon, who believe that language is more of an epiphenomenon than a single evolved mechanism—in other words, that language is best described by (and, when we finally get out into space, best recognized by) its surface features, not its hypothetical mental structure. Along this line of thinking, if aliens have something we recognize as language in the first place, then it's probably going to be a language much like any other, with arbitrary association between symbols and meanings, discrete units ("words"), the ability to talk about new things and things that aren't there, and so on.
This is the same basic argument that many exobiologists use for extraterrestrial life: Alien life has to be a least a little bit like what we're used to or we'd never recognize it for what it is.
From this point of view, we can interpret Uhura's "three dialects of Romulan" a bit more loosely, more like she's saying that there are three major variations on the way the epiphenomenon of language is expressed. And this isn't so odd, when you think about it. Here on Earth, after all, we could say that we have at least two distinct ways of doing language—one auditory (spoken language) and one visual (signed language). Maybe on Romulus they've figured out a third way, like using touch, smell, taste, or another sense that humans don't even have?
Or maybe science fiction writers just need to learn a little bit more about linguistic diversity here on Earth before they set out to conquer the stars.