Andrea Camilleri is a very popular crime writer, as we all know, who hails from Sicily. He is known to add the odd sprinkling of Sicilian into his writing, but I do stress, it is just an odd sprinkling. He writes so that his primary readership (Italians) can understand his writing, and adds the occasional Sicilianism to add a touch of authenticity, to help plonk the reader into something which sounds that little bit more realistic.
This will occasionally involve a Sicilian word put into a normal Italian sentence, where the reader is likely to understand the meaning from the context.
Take this example from La forma dell'acqua: Sta tanticchia meglio, la febbre gli sta calando.
The word tanticchia is 100% Sicilian and I'm not even sure if there is any Italian word which is similar to it. It says that someone is now feeling a bit better. In Italian, you'd probably say something like: Sta un po' meglio.
Given it says that the fever has gone down, your average Italian reader is likely to be able to guess what tanticchia means in the context of the full sentence.
Importantly, the remainder of the sentence is Italian, it's just one Sicilian word which has been put in place of the Italian term. If we were to say the whole sentence in Sicilian, it would look something like this:
Sta tanticchia megghiu, 'a frevi cci sta calannu.
An Italian might still be able to work out what that meant in the context of the whole story, but the readability diminishes, it's too big a distraction for the reader trying to enjoy the story. Camilleri manages to add a touch of realism by just dropping in one obvious Sicilian word which doesn't slow the reader down too much (although most will have to pause a tiny bit).
At least that was a real Sicilian word, properly spelt, grammatically correct in terms of where it was placed in the sentence. Many times, Camilleri uses other techniques where he is not actually using real Sicilian words, he's using a semblance of a Sicilian word. It might be an Italian word but he has given it a Sicilian ending, or it's a Sicilian word which has been Italianised to the extent that it looks like its Italian equivalent (but the reader will see that it's not quite correct Italian). Once again, a similar thing is happening, Camilleri is injecting a tiny bit of exoticism without risking that the reader will lose the flow of the story.
Some examples follow from the same book.
<<Che c'e? Che minchia vuoi? Che ti piglia?>>
Che c'è would probably come across sufficiently lowbrow (more commonly an Italian would use the fuller Che cosa c'è) and is a bit reminiscent of a Sicilian asking: Chi cc'è?
minchia is a typical Southern swear word that is probably known to most Italians.
Now piglia is an interesting one. The verb pigliare is an Italian word, but I'm not sure how common it is used in Italy in place of prendere, I would guess that it's a bit archaic.
The Sicilian for prendere is pigghiari. Now while in some parts of Sicily one might hear pigliari instead of pigghiari, I would say that Camilleri opts for pigliare because it's going to appear slightly unusual to the average Italian reader, making them feel as if they are immersed in a Sicilian dialogue, but one which they have some chance of following without too much difficulty.
One last example
<<Allura?>>
<<Allura nenti.>>
In this example, the three words of this small exchange are all Sicilian words, but which are very similar to what the Italian would be, so the Italian reader would notice it was a bit different, but would understand the exchange immediately. The Italian would have been:
Allora?
Allora niente.
Actually, here's one last example:
Viene qua, garruso.
...omu di delinquenza
Si, c'inzirtasti.
Difficile che mi sbaglio cu tia.
garruso - I don't recognise this as an Italian word, so I am guessing that it's meant to be the Sicilian word: carusu, which means "boy", so Montalbano is ordering one of his policeman to come over, as in: get over here kiddo. But would an Italian understand garruso, and why has Camilleri tried to Italianise a Sicilian word? This is something he does often, with the result being a word that is neither Sicilian or Italian.
omu - Sicilian word for man, Italian = uomo. This one word is placed in the middle of a few lines of speech, just the one word in what is otherwise all Italian.
c'inzirtasti - Another interesting example. The Sicilian verb nzirtari means to guess, Italian = indovinare. Also, Camilleri is using the past absolute tense, which would rarely be used in Italian in this context, so it's a double whammy of exoticism. But would an Italian guess what c'inzirtasti means so readily? Also, Camilleri has Italianised it slightly, in Sicilian, it would look more like cci nzirtasti.
cu tia - in Italian, it would be con te. In context, an Italian would pick that up quite readily. Once again, a small injection of some Sicilianism into an otherwise Italian sentence, for that sense of immediacy.