With Italians it's pronunciation that's the problem.
There are too many meanings of "with", so I don't even know how to choose the meaning to explain this sentence. I am curious about how to understand the preposition ? On the basis of the sentence structure or what else? I hope some one can help me to understand and deduct the usage of "with"?
With this type of clause (see what I did there? :) ), the first thing I would do is try to reorder the words to see if I can make sense of why the "with" is there. I.e:
It's pronunciation that is the problem with Italians.
This helps you see why "with" is used.
For what it's worth, I think (generally speaking) it would be better to use "for" here, as "with" can sound a bit disrespectful.
For Italians it's pronunciation that is the problem.
(Though I don't know the full context of this single sentence.)
So, to understand the choice of "with" it is just a case of reordering the clause.
In the case of my poor attempt at humour at the start of this answer, I said:
With this type of clause the first thing I would do is try to reorder the words.
Why with? Well, try my technique of reordering the sentence to use a more typical order:
The first thing I would do with this type of clause is to try reordering the words.
The choice of "with" is harder, but as I said above, I think "for" might better". I'll explain a little bit:
The problem with
Expresses annoyance/frustration at a situation.
The problem with paying the bills is that you have to have all the money in your account.
The problem with Italians is their pronunciation (I can't understand them and that annoys me!).
Whereas "for" expresses a more neutral stance, explaining who (or what) a problem affects.
Pronunciation is a problem for Italians (unlucky for them).
The end of the month can be a problem for those with a low salary.
With Italians, it's pronunciation that's the problem.
The problem among Italians is pronunciation.
This Oxford Dictionaries page lists sixteen distinct, literal definitions of the preposition "with", along with eight idiomatic uses. Not a single one seems suitable for this sentence. Merriam Webster offers a larger and even more confusing set of choices. The example given for definition 2.f matches the pattern in your sentence, but the definition itself doesn't seem to apply.
Of course, a native speaker isn't likely to consult a dictionary for a common word like "with". Instead, we expect "with" to indicate something like accompaniment or other close association. We can generally determine a more precise association from context.
The other thing that we do is that we expect certain patterns. One common pattern is that words like "problem", "trouble" and "difficulty" are very often modified by "with" phrases.
Even though the following involve two completely different associations, the word "with" still matches that commonly expected pattern, and we can interpret each "with" to indicate whatever association makes sense:
Pronunciation is a problem with Italians.
Italians have a problem with pronunciation.
Even though "with", "for" and "among" mean very different things, these three sentences mean practically the same thing:
Pronunciation poses a problem with Italians.
Pronunciation poses a problem for Italians.
Pronunciation poses a problem among Italians.
