A dire il vero, voglio il cuoio.

It is a fixed expression meaning to tell the truth, truth be told, or to be honest.

Literally, it is something like at saying the truth, but you should learn it as an idiomatic phrase rather than translating each word too mechanically.

In this sentence:

A dire il vero, voglio il cuoio.

the phrase works like an introductory comment on the whole statement, similar to:

• To tell the truth, I want leather.
• Truth be told, I want the leather.

Because a dire il vero is an idiomatic expression built with the infinitive dire.

Italian often uses a + infinitive in set phrases, especially in expressions that comment on what is being said. Here, dire stays in the infinitive because the phrase is not the main action of the sentence. The main action is:

voglio = I want

So:

• A dire il vero = introductory phrase
• voglio il cuoio = main clause

In a dire il vero, il vero means the truth.

Italian often uses the definite article where English may not. So even though English says to tell the truth, the Italian structure is literally:

• dire = to say / to tell
• il vero = the truth / what is true

This is just the standard form of the expression. You normally do not say a dire vero here.

Yes, it is fairly common and sounds natural. It is a standard way to soften or qualify what you are saying.

Other similar expressions are:

• a dire la verità = to tell the truth
• in verità = in truth
• a essere sincero/a = to be honest

Of these, a dire il vero is perfectly normal and slightly polished or neutral in tone.

Voglio is the first person singular present tense of volere.

So:

• io voglio = I want

Some forms of volere are:

• io voglio = I want
• tu vuoi = you want
• lui/lei vuole = he/she wants
• noi vogliamo = we want
• voi volete = you all want
• loro vogliono = they want

In this sentence, the subject io is omitted because Italian often leaves out subject pronouns when the verb ending already makes the subject clear.

Italian often uses the definite article with nouns in places where English may or may not use one.

So il cuoio can mean:

• the leather
• leather, depending on context

If you are talking about leather as a material in a general sense, Italian very often still uses the article:

• Mi piace il cuoio. = I like leather.

In your sentence, voglio il cuoio most naturally sounds like I want the leather or I want leather, depending on context.

Not exactly.

• cuoio = leather, especially the processed material
• pelle = skin or hide, and sometimes leather in broader use depending on context

In many contexts:

• scarpe di cuoio = leather shoes
• giacca di pelle = leather jacket

So there is some overlap, but cuoio usually points more specifically to leather as a treated material, often with a slightly tougher or more traditional feel.

Grammatically, yes. Contextually, it can sound a little unusual on its own, because I want leather is a very specific statement and usually needs a situation around it.

For example, it would sound more natural in contexts like:

• choosing materials for shoes or furniture
• specifying a preference in a shop
• talking about craftsmanship or fashion

Without context, the sentence is correct but a little odd, simply because the object leather is very specific.

Cuoio can be tricky for English speakers because of the vowel sequence.

It is pronounced approximately:

KWOH-yoh

More carefully, it is usually divided like:

cuò-io

The stress falls on the first part:

CUO-io

Try not to pronounce every vowel as a fully separate syllable in an exaggerated way. Listen for a smooth transition from cuo to io.

Yes, but it is most natural at the beginning, set off by a pause:

• A dire il vero, voglio il cuoio.

You may also hear it after the main clause, though that is less common and more stylistically marked:

• Voglio il cuoio, a dire il vero.

Putting it first is the safest and most natural choice for learners.

They are very similar and often interchangeable.

• A dire il vero = to tell the truth / truth be told
• A dire la verità = to tell the truth

A dire la verità may feel slightly more transparent to learners because la verità clearly means the truth as a noun.
A dire il vero is a very established expression and can sound a bit more idiomatic or refined.

Both are correct and common.