La infermera diu que la pacient ha d'esperar abans d'entrar.

Because the sentence is talking about a specific nurse and a specific patient: the nurse and the patient.

In Catalan, the definite article is used normally with specific nouns:

• la infermera = the nurse
• la pacient = the patient

A useful contrast:

• La infermera diu... = The nurse says...
• És infermera. = She is a nurse.

So when it is someone’s role or profession in general after ser, Catalan often has no article, but when you mean a particular person, you use one.

Because pacient is a common-gender noun in Catalan: the form stays the same for masculine and feminine, and the article shows the gender.

• el pacient = the male patient
• la pacient = the female patient

This is common with some nouns ending in -ent, such as:

• el/la pacient
• el/la estudiant
• el/la cantant

So the feminine is not made with -a here.

Diu is the 3rd person singular present of dir, which means to say.

So:

• jo dic = I say
• tu dius = you say
• ell/ella diu = he/she says
• nosaltres diem = we say
• vosaltres dieu = you all say
• ells/elles diuen = they say

In this sentence, La infermera diu... means The nurse says...

Que introduces the clause that follows diu. It works like English that in The nurse says that...

So the structure is:

• La infermera diu = The nurse says
• que la pacient ha d'esperar... = that the patient has to wait...

In English, that is often omitted:

• The nurse says the patient has to wait.

In Catalan, que is normally kept, so diu que... is the usual pattern.

This is the Catalan structure haver de + infinitive, which expresses obligation or necessity.

• ha de = has to
• esperar = wait

So:

• ha d'esperar = has to wait / must wait

More examples:

• He de marxar. = I have to leave.
• Han de venir. = They have to come.

This is one of the most common ways to say have to in Catalan.

Because de becomes d' before a vowel.

So:

• de + esperar → d'esperar
• de + entrar → d'entrar

This is just normal apostrophe/elision in Catalan spelling.

You will see this very often:

• d'anar
• d'obrir
• d'estudiar

Because in Catalan, abans is normally followed by de when the next verb is an infinitive.

So:

• abans d'entrar = before entering / before going in

This is the standard pattern:

• abans de + infinitive

Examples:

• Renta’t les mans abans de menjar. = Wash your hands before eating.
• Ho pensaré abans de decidir. = I’ll think about it before deciding.

If a full clause follows instead, Catalan usually uses abans que:

• Espera abans que entri. = Wait before she enters.

No. La pacient is the subject of the subordinate clause, not the object of diu.

The sentence breaks down like this:

• Main clause: La infermera diu
• Subordinate clause: que la pacient ha d'esperar abans d'entrar

So the nurse is saying something, and what she is saying is: the patient has to wait before entering.

If you wanted The nurse tells the patient that..., you would need to mark that person separately, for example:

• La infermera diu a la pacient que... or more naturally in many contexts:
• La infermera li diu que...

Because Catalan often leaves subject pronouns out when they are not needed. The verb form usually makes the subject clear enough.

So instead of saying:

• Ella diu que...

Catalan normally just says:

• Diu que...

In your sentence, the nouns are already there:

• La infermera diu...
• la pacient ha d'esperar...

So adding ella would usually sound unnecessary unless you want emphasis or contrast.

Not always. Esperar can mean wait, but depending on context it can also mean expect or hope.

For example:

• Espero l’autobús. = I’m waiting for the bus.
• Espero que vingui. = I hope he/she comes.

In this sentence, esperar clearly means wait, because it is followed by abans d'entrar, which gives a time sequence:

• ha d'esperar abans d'entrar = has to wait before entering

Yes. Ha d'esperar can often be translated as either has to wait or must wait, depending on the tone you want in English.

• has to wait sounds a bit more neutral or everyday
• must wait can sound slightly stronger or more formal

In Catalan, haver de + infinitive covers that idea of necessity, and English translation depends on context.