They don't talk good like us.

With a century or more time scale, you're entering the realm of the language itself changing, forget mere slang. A slippery slope that makes the writer cling to the walls by the fingertips.

What would teenage slang consist of in a hundred years?

This was a question posed of a writer looking to do a little brainstorming in a fiction group over yonder.  At the risk of being judgemental at all, I think s/he is being a little naive.  That question is an exploding can of foam-rubber snakes spraying in every direction.  Why?  Because slang is the love child of evolving language and changing culture.  Characters a 100 years from now will have new slang words…but their “plain and simple” English will be strewn with vocabulary that will baffle we folk in the early 21st century.

For instance:

The merry chirp of a cell interrupted the debate of cutest professors on campus.  The three young ladies all listened for the second chirp.  Melanie and Rachel relaxed back into their chairs.  That wasn’t their ringtone.  Allison half-rose out to dig her cell out of her back pocket, checked the screen and brought it to her ear.  

     “Hi, Mom.  Just hanging out with the girls at Starbuck’s.  No, we’ve got tickets to the last 3D movie of the summer.  Then we’ll grab some pizza and head to Rachel’s.  Really?  Thanks.  Love you too.”

     Allison tapped her cell and picked up her iced mocha.  “We got to scoot.  Mom saw on the news that there’s a pile-up on the freeway.  We’re gonna have to go surface to the cineplex to avoid it.”

“Yikes!”  The other girls jumped to their feet.  Melanie clicked her key and her car beeped to life.

The above vignette is my ad-lib attempt to write a reasonable scene set in 2016 with zero-to-minimal use of anything that could be called “slang”.  Yet, how would it read to someone in 1916?  Even assuming a very aware and knowledgeable individual, they’d be frowning mightily as they puzzled out the sentences.  “Car” and “movie” both existed as words, but only for a few years as of 1916.  “Pizza” was a unique ethnic food known only to those with adventurous palettes in cities big enough to have a “Little Italy” area.  “She saw the news” rather than “read” or “heard”?  What does that even mean?  Since they are referring to a car, perhaps “freeway” is some sort of roadway?  “Starbuck” is a character in “Moby Dick”.  Has the name made some sort of resurgence?  A woman with a “back pocket” on her dress?

Because the readers are stuck with 21st century (in my case) English, any future or alien world has to be predominantly presented in 21st century English.  Writing is all about picking the right word.  This exercise is creating and picking at the same time.  Which words to insert in the normal flow of English to denote a gizmo or a food or a sense organ that conjures a strange new world for the reader?  It’s linguistic poetry to manufacture a word that sounds authentic and tastes right on the tongue.  Too many SF writers, especially of the Good Old Days, didn’t really take the trouble in picking or creating these words as they pounded the keyboards.  Well, they had hard deadlines to meet.

To make up a world with new language sprinkled on top of English is a challenge.  To make up new slang is another step beyond.  So you’ve invented (for example) a “hoverboard”.  It replaces skateboards and snowboards in this future world.  Snowboarders are called “shredders” because they tend to tear up the snow, making the slope unfit for skiing.  You have to sit and nurture your imagination to how these hoverboards work and are there side effects and what sort of person-personality to they attract?  And then try to make up a new “shredder”.

Whew.

Damn it’s fun to do.