Some of the effects get lost as the passing from the neapolitan accent which can't be rendered simply with an english translation (apart from the letter scene, where the client mangles the language but with an another accent, while in the english translation of course you just have the mangling). In the scene of the introduction of the sham nobles to the Loren's father the 4 impersonators speak with a kind of refined italian by, for example, making open vowels closed. And so on.
That's kind of what I figured. It must be like the way the Abbot and Costello classic jokes wouldn't translate I suspect. Stuff like Who's On First and the Racehorse joke below.
Lou Costello: I just bought me a racehorse and I gotta take care of him. What do you feed a horse anyway?
Bud Abbott: Well, a horse eats his fodder.
Lou Costello: He eats his father?
Bud Abbott: Certainly.
Lou Costello: That?s fine. Then what does his father eat?
Bud Abbott: He eats his fodder.
Lou Costello: Well, whata ya know! Then what does the horse?s mother eat?
Bud Abbott: She eats her fodder.
Lou Costello: What are they ? cannibals!!?
Bud Abbott: Certainly not. Every horse has to eat his fodder.
Lou Costello: Oh, I see. He eats his father and then his father eats his father and his mother eats her father and, before you know it, there won?t be no fathers left for Father?s Day!
Bud Abbott: No. No. To feed a horse you take a bag and put his fodder in it.
Lou Costello: You mean you put his father in a bag?
Bud Abbott: That?s right, and you hang his fodder on his nose.
Lou Costello: Now ain?t that a pretty picture ? a horse walking around with his father hangin? on his nose!
Bud Abbott: Well, if you?re gonna run him in a race, if the track is wet will he run well?
Lou Costello: I think so ?
Bud Abbott: What I?m asking is .. . is he a mudder?
Lou Costello: How can he be a mudder? Ain?t a she always a mudder?
Bud Abbott: Certainly not. Sometimes a he makes a better mudder than a she.
Lou Costello: Whata you know. Look, suppose the mama horse has little horses, does that make her a mudder?
Bud Abbott: Well, that depends on her feet.
Lou Costello: Ya learn sumpin? every day, don?t cha?
Bud Abbott: A mudder is a horse that likes to run in mud on account of having sore feet.