For those of you paranormal or sci-fi romance writers about to exit the page because you don't think this applies to you, think again. There are many parts to language which you need to include in your book. Just to be contrary, I'll leave the part concerning paranormal writers until the end.
Fantasy romance writers, this part is for you. If you've thought up a fantasy world, likely you've realized that your characters don't speak English. But when is it appropriate to add in another language?
In truth, it should only be done as necessary. You decide that, not me. If it furthers the plot in some way, it is necessary. If you have a word in that language which doesn't translate into English, it is necessary. An example would be the name of a certain kind of food, plant, or animal which is completely different from any food, plant, or animal on Earth. The occasional phrase or foreign word can add to the authenticity of your world, but if you add too much, it can become too confusing and your readers will start to put the book down. I'll never forget reading A Clockwork Orange by Anthony Burgess. Whether or not it deserves the name of classic, I'll never know. I couldn't finish the first page. The language used confused me too much.
I'm not a linguist, but one thing I can say about your language itself is be consistent. Don't put choppy sounding words in your character's speech if her language sounds melodious. Try out the words on your own tongue first, to make sure they sound good, and try to come up with a rough grammar scheme at least, even if you're only using one phrase. If you're only punctuating your text with a single word here and there, of course you won't need to think about grammar, but otherwise it should be one of your top priorities.
That being said, let me move on to the part of language some of you have been perched on the edge of your chairs waiting for me to explain: slang. Yes, slang. It isn't brilliant, but it is necessary to your story. Fantasy and sci-fi romance writers should create slang based on the atmosphere of their world. Like language, it shouldn't be detrimental. More formal worlds will use less slang and more proper grammar, while slum-like worlds will use more slang and likely swearwords, to boot. But what about paranormal romance writers? You aren't excluded from this, you know. Even if it's only one sentence or two per book, it adds to the feel of a book. Would Lynsay Sands's Argeneau series have had the same impact without the term "feeding off the hoof?" I suppose it is possible, but that one phrase makes the book come to life. If your world has another society (which if it is paranormal, it does), it needs to have some form of language which differs from the real world. Most times, that means slang.
Up next: L. K. Below blogs about how to separate your fantasy or alien world from Earth.