La traduzione di questa frase non è difficile, ma voglio che suoni naturale.

Because di is the normal way to express of in Italian.

• la traduzione = the translation
• di questa frase = of this sentence

So la traduzione di questa frase literally means the translation of this sentence.

Italian uses this structure very often:

• il titolo del libro = the title of the book
• la fine della storia = the end of the story

The article la means the, and here it sounds natural because we are talking about a specific translation: the translation of this particular sentence.

Italian uses articles more often than English does, so where English might sometimes say translation, Italian will often prefer la traduzione.

Both are possible, but they do not sound exactly the same.

• non è difficile = it isn’t difficult
• è facile = it’s easy

The version with non è difficile is a little softer and more cautious. It suggests:

• the task is manageable,
• but maybe the speaker still cares about getting it exactly right.

That fits well with the second half of the sentence: ma voglio che suoni naturale.

Because che introduces a subordinate clause.

Here the structure is:

• voglio = I want
• che suoni naturale = that it sound natural

So voglio che... means I want that... / more naturally in English, I want ... to ...

This is a very common Italian pattern:

• voglio che venga = I want him/her to come
• voglio che sia chiaro = I want it to be clear

Because after voglio che, Italian normally uses the subjunctive.

So:

• suona = indicative
• suoni = present subjunctive

The verb here is suonare, and the present subjunctive form for lui/lei is suoni.

This happens because volere che expresses a wish, intention, or desire, and that usually triggers the subjunctive:

• voglio che sia = I want it to be
• voglio che sembri = I want it to seem
• voglio che suoni = I want it to sound

It can mean those things, but it also means to sound in the sense of how words or language come across.

Here, suoni naturale means sounds natural.

Some examples:

• Questa frase suona strana. = This sentence sounds strange.
• Suona bene in italiano. = It sounds good in Italian.

So in this sentence, suonare is being used metaphorically, just like English sound.

Because Italian often leaves out subject pronouns when the subject is clear from context.

In this sentence, the understood subject of suoni is la traduzione.

So the full idea is:

• voglio che la traduzione suoni naturale

But once la traduzione has already been mentioned, Italian can simply omit it.

This is very normal in Italian and one of the biggest differences from English.

Because after verbs like sembrare, apparire, and suonare, Italian usually uses an adjective, not an adverb.

So:

• suona naturale = it sounds natural
• not suona naturalmente for this meaning

Naturalmente means naturally, but that usually refers to the manner of doing something, not to how something seems or sounds.

Compare:

• Parla naturalmente. = He/She speaks naturally.
• La frase suona naturale. = The sentence sounds natural.

Yes, it does.

The subject is la traduzione, which is feminine singular, and the adjective should agree with it. But naturale has the same form for both masculine and feminine singular, so you do not see a difference here.

Compare:

• la traduzione suona naturale = feminine singular
• il testo suona naturale = masculine singular

Both use naturale.

But in the plural, you can see the agreement more clearly:

• le traduzioni suonano naturali
• i testi suonano naturali

Yes, but the meaning shifts slightly.

• voglio che sia naturale = I want it to be natural
• voglio che suoni naturale = I want it to sound natural

sia naturale is more general: the translation should be natural overall.

suoni naturale focuses specifically on how it comes across when read or heard. For a translation, that is often exactly the nuance you want.

Yes, it is natural and correct.

It sounds like someone saying:

• the translation itself is not hard,
• but making it sound idiomatic is important.

A slightly more explicit version would be:

• La traduzione di questa frase non è difficile, ma voglio che la traduzione suoni naturale.

However, repeating la traduzione would be unnecessary, so the original version is smoother.

Because frase is the normal word for sentence in this context.

• frase = a sentence or phrase in everyday language/grammar discussion
• sentenza usually means a judgment, verdict, or sometimes a formal saying/maxim

So if you are talking about translating a sentence in a language-learning context, frase is the natural choice.