Slang is an incredibly tricky topic in fiction, including stuff set in the real world. Used correctly, it can be powerful tool for vividly evoking a sense of place, time, and class: a common Brooklyn laborer in 1950 and a rich California teenager in 1980 are going to use wildly different idioms in their casual speech. But used incorrectly . . . I once bounced right out of a Regency-set fantasy novel whose heroine talked like a character from Buffy the Vampire Slayer, because it kept undermining my sense of the setting. Not every novel has to precisely replicate the speech of its era, of course; that’s a very specific game, and not one every story is interested in playing. Like the movie A Knight’s Tale opening with its medieval peasants singing “We Will Rock You” at a joust, you can advertise up front that your goal is to create a different effect entirely. But not everyone has the chops to pull it off, and when they fail, it falls very flat indeed.
But what about secondary-world fiction? The game there is even more complicated. Most of us tend to write “neutral” prose, avoiding obvious markers of our time period. Nobody in a 1980s Tolkien clone ever said “radical, dude.” (At least not that I’m aware of, and now I find myself really wanting to know if that does exist. Portal fantasies don’t count.) Of course, the illusion of neutrality is just that: an illusion. Everything about how we talk and write is tinged with the flavor of one era or another, and if you don’t make a concerted effort to ensure the era in question is a different one, it will probably be identifiable decades later as belonging very much to the 1980s or the early 2000s or whenever. This pervades the text on a level down to the sentence structure and punctuation: after five years of writing the Memoirs of Lady Trent, I’m still in the process of scrubbing the Victorian influence out of my prose, and if you look at these blog posts you’ll still find them peppered with colons and semicolons and other markers of nineteenth-century diction. (Seriously, I can’t get rid of them. I’ve tried.)
Let’s leave behind the nitty-gritty bits like punctuation, though, and look at idioms more generally. What kinds of speech do we put in the mouths of our characters, and how can that help (or hinder) the worldbuilding?
Going back to Tolkien clones for a moment . . . the use of cod-medieval English in a certain type of epic fantasy used to be so widespread that we even have a slang term for that, saying the characters are speaking “forsoothly.” Most of the writers who attempted to do this lacked Tolkien’s ear for the rhythms of such speech, or even basic knowledge of its rules, which is why this is so easily parodied. If you’re going to imitate the diction of a historical period, you need to immerse yourself in real examples, or else stick with that “neutral” prose; the latter is way less distracting than a bad attempt at the former. As a result, you find very little “forsoothly” speech in most modern fantasy, even when the setting is meant to be more or less European-medieval. In fact, you’re more likely to see the opposite: a certain flavor of “gritty,” profanity-laden, modern-style language, meant to strip away the nostalgic haze that used to overlay such depictions. As a corrective I see why it happened, and it can be done well; on the other hand, after a while it becomes just as predictable and open to parody as its predecessor.
So maybe you look at your options and think, I don’t want to write in Ye Olde Englisshe, but I also don’t want it to sound like I’ve dropped the cast of The Wire into a fantasy world. Can I invent some slang?
. . . good luck with that.
It can be done. And the people who pull it off well are brilliant. It’s easy to forget, but the slang of Buffy the Vampire Slayer sounds realistic less because it imitated its period than because lots of people started talking like the show. The novel and film of A Clockwork Orange use Nadsat, a Russian-influenced argot that strongly contributes to the three-dimensionality of its invented future subculture. Russell Hoban took things even further with Riddley Walker, where the entire novel is written in an imaginary future dialect of English.
But most of us aren’t going to go that far, and would face-plant if we tried. Instead we just salt in a few terms here and there, as suits the story we’re telling. Robin McKinley does such a good job with this in Sunshine that I curse myself for not thinking of it first; in that urban fantasy setting, much of the slang is mythological in origin, with the narrator saying she’s “thor as hell” when she wants to describe her strength, or talking about charms “going kali” when they become unstable. “Spartan” is an all-purpose word in the vein of “cool” or “great.” Even if your story isn’t set in a variant on the real world, you can look for things in the religion or history or environment of the characters that might give rise to equivalent terms.
It’s possible to fall down a rabbit-hole when you try to do this. If I recall correctly, Marissa Lingen has described this as the “moss-troll ichor” problem. You want to describe something as being the exact shade of green found in Nyquil, but there’s no Nyquil in your world, so instead you say it’s the green of moss-troll ichor — but your reader doesn’t know what shade of green that is, and furthermore now you’ve added moss-trolls to your setting just for the sake of a description, and maybe you need to put some onstage so that the reader will understand what color their ichor is, and for crying out loud, all you wanted to do was say something was a very deep blue-tinged green color . . . which is why most writers will only put in a few touches of invented slang, where it will be the most useful.
Readers’ mileage on this varies. Some find invented slang incredibly distracting, and would prefer you just use “normal” English. Others will be kicked right out of a secondary-world fantasy if anyone says “okay,” because to them that is too specifically modern. Some people feel you shouldn’t use words like “galvanize” in a setting where there was never any Luigi Galvani, while others have no idea that’s the etymology, or wouldn’t care if they did. There’s no pleasing everyone, and the more you try, the more bland and flavorless your prose is likely to become. So by all means, stop and look at the metaphors your characters use to describe things, the touchstones they use for praise or condemnation, and ask whether changing those up can add depth to your world.