Leigh Bardugo's Grishaverse is a fully detailed fantasy world with several different countries - all of which have small cultural backgrounds and details of their own. As a result, the Shadow and Bone series shows several different languages, currencies, and skills.
The show-runners even managed to sneak in references to the real-world books, such as the Apparat's copy of Lives of the Saints. If fans are quick enough, they will also be able to see all the other ones as many appear in blink-and-you-miss-it moments.
Shadow And Bone: The Book
Linguist David Peterson created a written Ravkan language, and a Ravkan edition of Shadow and Bone shows up in a blink-and-you'll-miss-it show moment. When the Crows are carjacking General Kirigan's carriage, Jesper opens the door on David Kostyk, who panics for and throws a book at him.
That book turns out to be Shadow and Bone. Jesper handles it in an exasperated fashion when he complains about David, and after that, it disappears. That said, it was an excellent moment and a great easter egg.
The DeKappel
In the first episode, Kaz is stopped in the Crow Club by one of his associates, Rotty, to discuss the recent stealing of a valuable oil painting by DeKappel called "The Fold." As noted in the title, it depicts the Shadow Fold that crosses Ravka.
As Kaz leaves Rotty after saying he'll keep an eye out for the thief, the audience sees the painting on one of the walls in his office. This both sets up what a master thief Kaz is, and also gives the audience foreshadowing for Kaz's own trip into the Fold.
Money
The first scene involving the Crows takes place at The Crow Club. Jesper is gambling, and during this scene and the following one, the audience clearly sees different currencies on the table. They all look suitably different from one another, with paper money folded amongst coins.
Jesper also mentions that Zemeni coin can withstand being shot by a bullet, and thus hunts out a counterfeiter at the tables with him. Currencies that are made of different materials are yet another way that Bardugo and the showrunners expanded the world.
Crow Club Shares
When Kaz is putting together his crew for the Sun Summoner heist, he knows he'll need Inej. She's an expert with knives, and he's grown used to working with her. Therefore, he needs to find a way to try and recruit her.
Kaz does this by offering his shares in the Crow Club, which are covered in the written Kerch that the conlangers, David Peterson and Christian Thalmann, came up with for the show. Considering Bardugo admitted in a Q&A that Kerch is loosely based on The Netherlands, one of the main trading countries in the world, Kaz making deals and exchanging his shares for his business fits well with the setting.
Kaz's Cane
True to the books, Kaz Brekker's cane has a crow's head for a handle topper. This is fitting since he works at an organization called the Crow Club. Kaz uses it quite a few times through the series to knock items away and get himself around (among other things).
However, the cane is used differently in the Shadow and Bone book, as Kaz has used it ever since he fell off a roof and broke his leg. Though it's just another prop, it also works as Kaz's weapon in addition to his sleight of hand and his wits. It's an easy enough thing to let the eye pass over, though.
Inej's Knives
The only time the audience gets a really good look at Inej's knives is when Tante Heleen attempts to divest her by taking away her weapons. She has several, all named after the saints. Alina even gives her a knife, which Inej names after her. While Inej's ability to climb and hide, to the point of invisibility, is useful, her knives are her primary weapon.
In the Six of Crows novels, Inej's knives also play a similar role in her life. They make up a large part of who she is since they encompass both her faith in the saints and serve as her weaponry.
Jesper's Guns
There are several great costumes on Shadow and Bone, with some full of hidden details. Jesper's guns are particularly fascinating; according to promotional material on Reddit, they have a gold inlay. They were also created by an antiques gunsmith who came out of retirement so he could work on them (via Reddit). They end up saving the day when the Crow crew needs to cross the Fold, as Jesper attempts to shoot at the volcra so the crew will be left alone.
Jesper uses them throughout the various scrapes that the Crow crew gets into throughout the season. His prowess as a sharpshooter is a large part of the reason why Kaz recruits him in the first place. The guns, despite simply being weapons, help quite a lot during the show.
Languages
Peterson and Thalmann created and visualized the languages of the Grishaverse. In a Reddit AMA, the two explained that Thalmann and Peterson created the Fjerdan language together, with Peterson also writing the Ravkan and Kerch language. There is no spoken Kerch at this point. The maps also show the Shadow and Bone fans where each country is in relation to one another.
Written Ravkan can be seen on the cover of the Ravkan edition of Shadow and Bone that David throws at Jesper in an attempt to startle him before getting away during the attack on the Darkling's carriage. Though most of the dialogue is in English, the glimpses the audience gets of spoken language, mainly Fjerdan, serve to flesh out the world.
Ketterdam Phrases
"The deal is the deal" and "No mourners, no funerals" are two phrases used by the Crows throughout the series. They are brought over from the book series featuring the group, aptly titled Six of Crows. The first is used when completing a piece of business and is used by Kaz the most.
The second is more enigmatic. Kaz and Inej share the phrase as a crew before the final badass showdown on the skiff. Essentially, it's the criminals' way of saying "good luck" and hoping that no one dies; that way, no one has to attend a funeral. Adding slang and cultural jargon to Ketterdam more fully fleshes out its merchant atmosphere.
Materialki Leigh
When Alina is first introduced at the palace, the Grisha embrace her immediately after her performance. The first to do so is a blonde in a purple Materialki kefta, who is none other than the creator of the world herself, Leigh Bardugo.
Hiding her in the rest of the Grisha at the palace is also a clever way to bring her in for a cameo; she can be in the show without drawing too much attention, quite like the way Alfred Hitchcock would cameo in his films.