Poeta dicit carmen novum de rege et regina mox scripturum esse.

The sentence has two parts:

• Poeta dicit = The poet says
• carmen novum de rege et regina mox scripturum esse = the thing he says

So the overall structure is:

• main clause: Poeta dicit
• indirect statement: ... scripturum esse

This is a very common Latin pattern after verbs like dicit, putat, scit, audit, and so on.

Because after dicit, Latin normally uses an indirect statement.

In English, we often say:

• The poet says that he will soon write...

In Latin, instead of using a separate that-clause, classical Latin usually uses:

• an accusative subject
• plus an infinitive

Here, the infinitive is scripturum esse, which means to be going to write or, more naturally in English, will write.

So Latin expresses he says that he will write with an infinitive construction rather than with a word exactly like English that.

Scripturum esse is the future active infinitive of scribere (to write).

It is formed from:

• the future active participle: scripturus, -a, -um = about to write / going to write
• plus esse = to be

So:

• scripturum esse literally means to be about to write
• in smoother English here, it means will write

This is the normal way Latin shows future time inside an indirect statement.

Because the participle in an indirect statement agrees with the subject of the infinitive, and that subject is understood as accusative.

In a full version, Latin could say:

• Poeta dicit se carmen novum de rege et regina mox scripturum esse.

Here:

• se = himself
• scripturum agrees with se
• both are masculine accusative singular

So scripturum is not nominative; it is accusative because it belongs to the infinitive clause.

It is understood.

The full sense is:

• Poeta dicit se ... scripturum esse
  = The poet says that he will write...

Latin often leaves out se when it is easy to understand that the subject of the infinitive is the same as the subject of the main verb.

So here the understood subject is:

• se = himself, referring back to poeta

That is why the sentence means:

• The poet says that he will soon write a new poem/song about the king and queen.

Carmen novum is the direct object of scribere.

The poet is going to write what?

• carmen novum = a new poem/song

A few details:

• carmen is a neuter singular noun
• it is accusative singular here, though for carmen the nominative and accusative look the same
• novum agrees with carmen in gender, number, and case

So:

• carmen = poem/song
• novum = new
• together: a new poem/song

Because they are governed by the preposition de, and de takes the ablative.

So:

• de rege = about the king
• de regina = about the queen
• de rege et regina = about the king and queen

This is a standard rule:

• de + ablative

Here the phrase tells us the topic of the poem.

Mox means soon.

It modifies the idea of scripturum esse, so the sense is:

• will soon write

Latin word order is flexible, so mox can stand in different places without changing the core meaning very much. Here it sits near the infinitive phrase and naturally goes with the future action.

To an English speaker, yes, it can feel unusual, but it is perfectly normal Latin.

A more word-for-word layout would be something like:

• The poet says a new poem about the king and queen soon to-write-to-be.

That sounds strange in English because English relies much more on fixed word order. Latin relies more on case endings and standard constructions like the indirect statement.

So the order here is natural Latin, even though English would normally rearrange it.

Yes. Carmen can mean song, poem, verse, or even more broadly a composition in verse.

Which English word is best depends on context. In many learning sentences, poem is often the safest choice, but song can also be possible.

Yes. A very helpful expanded version is:

• Poeta dicit se carmen novum de rege et regina mox scripturum esse.

This makes the hidden subject explicit:

• Poeta = the poet
• dicit = says
• se = himself / that he
• carmen novum = a new poem
• de rege et regina = about the king and queen
• mox = soon
• scripturum esse = will write

For many learners, seeing the sentence this way makes the indirect statement much easier to understand.