Post procellam omnes de naufragio diu loquuntur.

Because post is a preposition that takes the accusative when it means after.

• post procellam = after the storm
• procella is a first-declension noun
• its accusative singular form is procellam

So this is a standard prepositional phrase: post + accusative.

Because de normally takes the ablative.

• de naufragio = about the shipwreck
• naufragium is a second-declension neuter noun
• its ablative singular form is naufragio

So de + ablative is the normal pattern for about/concerning.

Because loquor, loqui, locutus sum is a deponent verb.

Deponent verbs:

• have passive forms
• but active meanings

So loquuntur looks passive, but it means they speak or they talk, not they are spoken.

Loquuntur is:

• 3rd person plural
• present tense
• indicative mood
• from the deponent verb loquor

So it means they are speaking / they speak / they talk.

Because it is plural, it matches omnes.

Latin omnes literally means all or all people here, so it takes a plural verb.

• omnes ... loquuntur = all are talking
• English may translate this naturally as everyone is talking, but Latin uses a plural idea

So the Latin grammar is based on all people, not on the English singular word everyone.

Omnes is nominative plural and is the subject of loquuntur.

It means:

• all
• or, more naturally here, everyone

Even though no noun like homines is stated, it is understood. So omnes by itself can mean all the people.

Diu is an adverb meaning for a long time or a long while.

It modifies the verb loquuntur:

• diu loquuntur = they talk for a long time

It tells us how long the action continues.

Latin often does not need a subject pronoun, because the verb ending already shows the person and number.

In loquuntur, the ending -ntur tells you the subject is they.

Here, the sentence also includes omnes, so the subject is already explicit. A separate pronoun would be unnecessary.

Yes, de can have several meanings depending on context, including:

• down from
• from
• about/concerning

Here, because it comes with a verb of speaking, de naufragio means about the shipwreck.

That is a very common use:

• de aliquo loqui = to speak about something

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

Putting the verb at the end is very common in Latin, especially in straightforward prose.

So:

• Post procellam omnes de naufragio diu loquuntur

is a normal Latin order, even though English would usually put the verb earlier.

Yes, often they could.

For example, these would still be understandable Latin:

• Omnes post procellam de naufragio diu loquuntur.
• De naufragio omnes post procellam diu loquuntur.

The basic meaning would stay the same, but the emphasis might change. Latin word order is often used for style and focus rather than strict grammar.

They are:

• post = after
• procella, procellae = storm
• omnis, omne = all, every
• de = about, concerning; from, down from
• naufragium, naufragii = shipwreck
• diu = for a long time
• loquor, loqui, locutus sum = speak, talk

Knowing the dictionary form helps you identify why the sentence uses:

• procellam instead of procella
• naufragio instead of naufragium
• loquuntur instead of loquor

Because the form omnes can be:

• masculine/feminine nominative plural = all people / all
• or masculine/feminine accusative plural

Here it is the subject, so it is nominative plural.

If Latin wanted to say all things as a neuter plural subject, it would usually be omnia, not omnes.

So omnes here clearly refers to people.

Grammatically, post procellam is a time expression meaning after the storm.

Of course, in context the storm is also the reason they are talking about the shipwreck, but the Latin phrase itself simply marks when this conversation happens, not explicitly why.