Iudex dicit mercatorem pretium minuere oportere.

Because Latin is using an indirect statement after dicit (says).

After verbs like dicit, Latin often uses:

• an accusative for the subject of the reported statement
• an infinitive instead of a finite verb

So in mercatorem pretium minuere oportere, mercatorem is the subject of the reported idea, but in an indirect statement that subject goes into the accusative.

So:

• mercator = the merchant
• mercatorem = the merchant, as the subject of an infinitive in indirect statement

In more literal English, the structure is:

• The judge says [the merchant ought to lower the price].

Latin expresses that as:

• Iudex dicit mercatorem pretium minuere oportere.

Because the sentence contains an indirect statement, and inside that statement oportere itself takes another infinitive.

Break it down like this:

• dicit = says
• mercatorem ... oportere = that the merchant ought / is obliged
• pretium minuere = to lower the price

So:

• oportere = to be proper / to be necessary / ought
• minuere = to lower

Together, minuere oportere means ought to lower or should lower.

A very literal rendering would be:

• The judge says the merchant to ought to lower the price

That is not good English, but it shows the Latin structure.

Oportere is an impersonal verb meaning something like:

• to be proper
• to be right
• to be necessary
• ought

In normal English, we usually translate it more naturally as:

• ought to
• should
• must (depending on context)

Here, the sense is:

• the merchant ought to lower the price
• or the merchant should lower the price

Even though oportere is impersonal in Latin, English usually makes it personal in translation.

Oportere often takes:

• a person in the accusative
• plus an infinitive

So the pattern is:

• aliquem aliquid facere oportet
• it is proper / necessary for someone to do something

In this sentence:

• mercatorem = the person affected
• pretium minuere = the action
• oportere = ought / should / must

So mercatorem pretium minuere oportere means:

• that the merchant ought to lower the price

Pretium is the direct object of minuere.

So:

• minuere = to lower, reduce
• pretium = price

Since minuere is a transitive verb, it can take a direct object. Here the thing being lowered is the price.

That is why pretium is in the accusative singular.

Because of meaning and syntax.

• dicit can introduce the whole indirect statement, but pretium is not the direct object of dicit.
• oportere does not directly govern pretium here.
• minuere is the verb that naturally takes pretium as its object: to lower the price.

So the internal structure is:

• mercatorem = subject of the infinitive phrase
• pretium = object of minuere
• minuere = infinitive dependent on oportere
• oportere = infinitive dependent on dicit

Because Latin usually expresses reported speech or thought after verbs like say, think, hear, know, etc. with an accusative-and-infinitive construction, not with a word meaning that.

So instead of:

• The judge says that the merchant ought to lower the price

Latin says, literally:

• The judge says the merchant ought to lower the price

But with Latin grammar:

• subject of reported statement → accusative
• verb of reported statement → infinitive

That is one of the most important sentence patterns in Latin.

Because iudex is the subject of the main verb dicit.

So:

• iudex = the judge
• dicit = says

That gives the main clause:

• Iudex dicit = The judge says

Everything after that is the content of what the judge says.

Minuere is the present active infinitive of minuere (from minuo, minuere, minui, minutum), meaning:

• to lessen
• to reduce
• to lower

Here it means to lower in the sense of lowering a price.

Because it is an infinitive, it does not show person or number by itself. The understood subject is mercatorem, supplied by the accusative-and-infinitive structure.

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

For example, these would still mean essentially the same thing:

• Iudex dicit mercatorem pretium minuere oportere.
• Iudex mercatorem pretium minuere oportere dicit.
• Mercatorem pretium minuere oportere iudex dicit.

The exact order can change emphasis, but the core grammar remains the same.

A learner should still notice the relationships by case and form:

• iudex = nominative subject of dicit
• mercatorem = accusative subject of the indirect statement
• pretium = accusative object of minuere
• minuere, oportere = infinitives

A very literal translation is:

• The judge says the merchant ought to lower the price.

If you want to show the Latin structure more clearly, you could expand it to:

• The judge says that it is proper/necessary for the merchant to lower the price.

Both capture the grammar, but the second one shows the force of oportere more explicitly.

It depends on context.

Oportere often suggests:

• what is proper
• what is fitting
• what ought to be done

So should or ought to is often the safest translation.

In some contexts, especially where there is authority, law, or obligation, English may use must. Since a judge is speaking here, the sentence could sound fairly strong, but grammatically ought to or should is still the basic meaning.

So a good default translation is:

• The judge says the merchant should lower the price.

or

• The judge says the merchant ought to lower the price.