I could probably translate it as "aiutante", like "helper"... Tha would do I guess. Thank you.
Let's get real. In the time period when barbershop porters existed, at least in the U.S, (first half of 1900's) barbershop porters were blacks, or as they were then called, Negros. They were not apprentices (at least in white-owned barbershops), and "helpers" is not really right. They took your winter coat or suit jacket and hung it up, and when your haircut was finished, they brushed any hair off your clothing, and helped you back into your jacket or coat, and might also shine your shoes. Now we might call them "flunky's," but that would avoid the primary purpose of the word, which was to indicate that the person was a Negro flunky.
That's exactly the kind of person we're talking about. I don't know how to translate it though.
I would probably go with the Italian for "negro servant." If there is an Italian idiom equivalent to "step 'n fetch it," that might also work.
I don't think this is an issue of political correctness but of accuracy in translation and basic logic.
I used to work as a porter in a hotel (in Britain in the 1970s - but the term is still in everyday use). You could argue that I was a 'flunky' but I would not have been happy to have been called a 'flunky' and 'flunky' cannot be used interchangeably with 'porter'. Similarly, even if in 1950s America most 'porters' were 'negroes' it isn't correct to assume that all 'porters' were 'negroes'. If the writer had meant to say someone was a 'flunky', of whatever race, they would have said so - so please find a term that is appropriate to whatever the author is saying. 'A barbershop porter' is a porter working in a barber shop - no more, and no less.
'porter' = job title
'flunky' = insult
As I said it's an issue about accuracy of translation. When you're considering which term to use you have to consider the positive, neutral or negative connotations of that term. If the author had meant to say 'flunky' they would have said 'flunky'.