One of the most effective and flexible tools a writer can employ to enhance their world-building is language. Creating a custom lexicon for your fictional universe doesn't mean you have to learn another language, either; you can rearrange and create new words out of ordinary English (or whatever language you publish in.)
This particular skill is one that most of us developed in childhood. As toddlers beginning to speak, we didn't know the proper name of everything. That's why that big thing in the driveway with four wheels that took Mommy away and brought her back again was a brrroom to me, named for the sound it made. Only later did it become a car. Words that are difficult for a toddler to pronounce often result in versions that are shortened, slurred together or replaced by similar sounds. This happens most frequently with names, which is why so many grandmothers are called something like Nanna, Nona, or Omah (in my family, the grandchildren call my mother Booma.) When Aunt Sheila proved too much of a mouthful for my grandniece, she dubbed me Enchilada.
As adults it's more difficult for us to let go of proper language and substitute or invent new terms, and for that reason when you begin world-building through language it can be a little daunting. Studying different forms of slang is one way to dust off your renaming skills; slang is usually colorful and sometimes has a kind of weird logic to it. When I began language world-building for Toriana I knew the British would have much more influence over my version of America, and it was no great leap to include the common language, so I started out with the UK slang I already knew as resource base and built out from there. Here's the "B" section from my Toriana Glossary:
bathboy: a male attendant/masseur who works at public baths for women
beater: a uniformed police officer who patrols the streets, usually on foot
believer: someone who believes in magic
belowground: beneath street level
binding: a stone or other object that can contain psychic energy until its release is triggered by touch or proximity
black: very strong, thrice-brewed tea
blackpot: a coal-fueled boiler
blacks: formal suit worn by high-class male servants
bloodbane: one of the highly toxic magic poisons used in snuffballs
blower: a chamber that uses air leeched from the city’s tubes to dry wet items
blue ruin: gin
blues: people of aristocratic birth
braves: warrior class of native Torian people
BrewsMaid: an automatic tea maker
bronze, bronzen: a theatrical cosmetic that temporarily darkens the skin
brown: Ttalian currency
bruiser: a large or physically intimidating man; thug
bucks: clothing made of buckskin
As you can see all of the words are made up of existing terms (barrister, blue ruin, braves, bum) or bits of words in English that I recombined or redefined (bathboy, blackpot, blower, BrewsMaid, bronzen.) So that my readers don't spend the entire reading experience flipping back and forth to the glossary I also focused on defining the terms in the context of the story. Here are three examples of how I used my Torian language from Her Ladyship's Curse:
I needed to replace the old coal boiler outside with an in-house furnace, but then walls would have to be torn out to convert the pipes, work for which no decent piper would barter. I was saving up for it, though, and in the meantime made do with what I could coax out of the old blackpot.
Out of respect for the real natives, I didn’t wear any feathers in my hair or on my person; those were reserved for braves who had bloodied themselves in war.
I sprayed my face, arms, hands, ankles, and feet with bronzen, which darkened my tanned skin to a copper brown.
There's more to world-building through language than simply manipulating words; you need to see your world and think about it from the perspective of someone who lives there. For example, when I had to name emergency response vehicles for Toriana, I thought about the fact that they don't yet have electricity -- so these vehicles can't have running lights or sirens. How then would they be instantly recognizable to the other drivers on the road? Logically color was the next best thing, so my medical emergency response vehicles are painted all-white, a very visible color. The use of white to paint a vehicle is also by law restricted to only medical emergency responders, so these Torian ambulances are the only white vehicles on the road. That led me to naming them whitecarts; white for the color + cart as a synonym for transport.
One important thing to remember when you're world-building through language is to always work toward reader-friendly words. Don't resort to a lot of gibberish just because it looks cool; you may speak your universe's language fluently but no one else does. Assuming your audience will psychically know exactly what you mean is a big mistake. So is clustering, or throwing five or six new words at the reader at a time -- avoid this by introducing your words singularly and defining them as best you can in context, too.
Building a language for your universe can be a fun writing exercise, and here are three methods I've used to teach students how to coin new words:
Action nickname: rename an occupation by substituting a nickname based on something they do at work (cop walking a beat = beater; printer of books = bookmaker)
Heard Words: change the spelling of your term to a phonetic representation of how it's spoken aloud by your characters (girl = gel; foreigner = furriner)
Shortening: remove one syllable or word from your term (tobacco = bacco; fortune teller = teller)
One final note: if you wish to invent entirely new words for your universe that are non-English and/or cannot be understood on sight, my advice is to limit the number and use them sparingly. To a reader these words are gibberish, and too much gibberish can kick your reader out of the story.