Regional dialect is basically writing what people speak. And, of course, people speak differently in different places. They have different customs and accents and idioms.
For example, I bring up the classic debate of "soda vs. pop". Where I'm from, it's soda. The idea of calling it "pop" makes me giggle. But in some other place in America, probably up North, calling it "soda" would make them giggle.
This doesn't just extend to vocabulary - think of the Southern tendency to drop the "g" off of some verbs: runnin', or hoppin', or jumpin'. Grammar and sayings are a large part of this. In America, we say we're just kidding, or we're messing with you. In Australia, they say they're just stirring with you. Also, don't forget brands - where we have Lays and Nestle, Australians have Shapes and Tim Tams. (I know this because my dad's family lives in Australia; my mother loves it when they send over Tim Tams.)
It's a bit much to comprehend, when you think about it. All those cultures out there... not to mention they change over time, so if your story takes place in the 1800s, you'll have to look up the dialect from that time period as well.
When making up your own regional dialect, for your Killonia or New Narnia, make sure it flows nicely. You don't explain it to your readers: just make it somewhat easy for them to follow. Like in American slang, "swag" is referred to when you're arrogant and cool and swaggering about the place like an idiot. *ahem* At least, that's what I've picked up on. No offense to any swaggers out there. (By which I mean, no offense to the swagger-type people who I might actually like.)
When you need for your world to be a personal, special, or realistic world, you have to write what the people say, how they say it. And you have to write it in a way that readers understand. When you do it right, your world becomes a better place for the readers glimpsing it.
So, that concludes my pretty short post. This isn't a terribly difficult topic to explain. It's only difficult when you're writing about a place you've never been, and as a writer of mysterious things, you should relish the challenge.
Enjoy the weekend, make good choices, and y'all have a blessed day!