Language is a powerful thing. So much is wrapped up in that word, so many divisions that separate and define people–Southern Americans versus Midwesterners, Cornish versus Cockney, etc. Any writer knows this. Achieving proper, distinct diction in writing can add a whole other layer to immersive quality.
Unfortunately, it takes time to develop the ear and the eyes in that direction. For the unwary reader, it can stumble them–look how many fumble with the Great Bard’s classic speeches and Twain’s twangs these days, and how many miss out on great works because of them.
I love colloquial speech, but especially in a fantasy world, where readers are already trying to settle their feet and get a feeling for the world they’ll be sifting through, I fear it can be too much. Good colloquialism is something that, when done well, is something you cease to notice very swiftly. But I dare say in mainstream fiction, or nonfiction, what have you, that colloquialism also comes with an innate ground: we have basic conceptions of Welsh, say, or German intonations, or Arabic. Even if we’ve never heard the phraseology before, most have already formed conceptions of the place or have some little knowledge of it: we ground the language firmly in that knowledge and do our best to move forward with it so located. We work toward its sounds from a different direction.
In a fantasy world, there is no such pre-existing “ground”. Many people also don’t have the patience to develop the means to interpret such. They want to dive into a world and be immersed, snap of your fingers, without the need to assemble a different sort of ciphering to get to that point. Thus, key words can be a better means, perhaps, to establish dialect and that sense of “the other” than full-blown colloquialism. It’s been something, I confess, to having battled my way through with The Hollow March and its sequels–how hard do I let the hammer of (often) class-based language barriers fall? The Nobles, with their precious jurti and guarded refinements, speak in a necessarily different version of the same tongue than many of the “Common Folk”. Most often, I have settled to let this come through in the use/non-use of contractions, older uses of similar words, with hardcore, jilting colloquialism reserved for specific characters: such as Chigenda, who has a very limited grasp of the language ANY of the other characters are tossing around him.
In the end, to any fellow writers reading this, I’d say in the end I’ve landed on a school of thought of using full-blown colloquialism at your own peril, as it may isolate you from some reader base. They’re there for the world, and above all, they want to understand it, be immersed in it; colloquialism is surely more immersive, but only once they’ve broken inside its external shell!