Potraje li oporavak dulje nego što očekujemo, razrednica će joj slati zadatke dok se ne vrati na nastavu.

This is a more formal or literary way to express a condition.

• Potraje li oporavak... = If the recovery lasts...
• A more neutral everyday version would be Ako oporavak potraje...

So verb + li here does not make a normal question. It creates a conditional meaning, similar to English Should the recovery last longer....

In this sentence, li is a particle attached to the verb to form a conditional-style clause.

So:

• Potraje li oporavak... = If the recovery lasts...

You may already know li from yes/no questions, but here it is used in a different structure. This pattern is common in more formal written Croatian.

Potraje comes from the perfective verb potrajati, while traje comes from the imperfective trajati.

The difference is aspect:

• trajati = to last, to be lasting
• potrajati = to end up lasting, to last for some time

In this sentence, Croatian uses the perfective verb because it refers to a possible future event with a result: the recovery may turn out to last longer than expected.

This is very common in Croatian: in subordinate clauses about the future, a present-tense form of a perfective verb often has future meaning.

Because in Croatian, the present tense of a perfective verb often refers to the future, especially in subordinate clauses such as:

• conditions
• time clauses
• purpose clauses

So here:

• Potraje li oporavak... literally looks present
• but it means If the recovery lasts / should last... in the future

The same thing happens later in the sentence with vrati in dok se ne vrati.

Nego što introduces a comparison clause.

• dulje nego što očekujemo = longer than we expect

Here:

• dulje = longer
• nego što = than
• očekujemo = we expect

In English, than is enough, but Croatian often uses nego što before a full clause.

You can think of it as:

• dulje nego što očekujemo
• literally: longer than what we expect

Even though that literal wording sounds odd in English, it is natural in Croatian.

Both mean longer.

In Croatian, both forms are used, but dulje is often felt to be more standard in many contexts, while duže is also very common in everyday speech.

So:

• dulje nego što očekujemo
• duže nego što očekujemo

Both are understandable and natural, though dulje fits very well in a standard written sentence like this one.

Razrednica is a female class teacher or homeroom teacher.

It comes from:

• razred = class, grade
• razrednica = female teacher in charge of that class
• razrednik = male teacher in charge of that class

So the noun tells you that the teacher is female.

Joj is the dative singular form of ona in its clitic form, and here it means to her.

In the sentence:

• razrednica će joj slati zadatke
• the class teacher will send her assignments

So:

• zadatke = the thing being sent
• joj = the person receiving them

That is why Croatian uses the dative.

Because će and joj are clitics, and Croatian clitics have special placement rules.

Here:

• razrednica is the first stressed word in the clause
• then the clitic cluster follows: će joj
• then comes the infinitive: slati

So:

• Razrednica će joj slati zadatke = correct

Croatian clitics usually cannot be placed freely the way full words can. Their position is much more fixed than in English.

This is the normal Croatian future tense, called futur prvi.

It is formed with:

• će
  • infinitive

So:

• će slati = will send / will be sending

Croatian often uses this structure where English uses will + verb.

Because slati is imperfective and suggests repeated or ongoing action.

Compare:

• slati = to send, to be sending, to send repeatedly
• poslati = to send once, to send off

Here the meaning is that the teacher will keep sending assignments during the recovery period, not just send one single set. So the imperfective slati fits better.

This is a very common point of confusion for English speakers.

In Croatian, after dok meaning until, the clause often contains ne, but it does not make the meaning negative in English.

So:

• dok se ne vrati = until she returns

It does not mean until she does not return.

You should learn this as a normal Croatian pattern:

• čekat ću dok ne dođe = I’ll wait until he/she comes
• ostat će tamo dok se ne oporavi = he/she will stay there until he/she recovers

So in this structure, ne is part of the grammar, not a separate logical negation.

It belongs to the verb vratiti se, which means to return.

Without se, vratiti usually means to return something or to give something back.

Compare:

• vratiti knjigu = to return a book
• vratiti se = to return, to come back

So in this sentence:

• dok se ne vrati na nastavu
• until she returns to classes

the se is necessary because the verb is reflexive here.

Because vratiti se na nastavu is the normal Croatian expression for return to classes / return to attending lessons.

Here nastava means teaching, lessons, classes. With this idea, Croatian commonly uses na.

So:

• vratiti se na nastavu = to return to school lessons / return to class attendance

This is best learned as a set phrase.

It is accusative plural.

The singular is:

• zadatak = assignment, task

The plural is:

• zadaci = assignments

As the direct object after slati, it becomes accusative plural:

• slati zadatke = to send assignments

Because Croatian usually does not need subject pronouns when the verb ending already shows the person clearly.

In:

• dok se ne vrati

the verb form already tells you it is he/she returns, and the context makes clear that it refers to the girl already mentioned by joj.

So Croatian often leaves out subject pronouns unless they are needed for emphasis or contrast.

Yes. A more straightforward version would be:

• Ako oporavak potraje dulje nego što očekujemo, razrednica će joj slati zadatke dok se ne vrati na nastavu.

This means the same thing, but many learners will find it easier because ako is more familiar than the formal verb + li pattern.