Korisnik će proveriti dostupnost tek kada bibliotekar otvori katalog.

In Serbian, the future tense is often formed with the clitic će plus the infinitive:

• korisnik će proveriti = the user will check

This is very common in standard Serbian.
You may also see a merged form in some contexts, especially with verbs ending in -ti, but with many verbs learners will most often meet the pattern:

• ja ću uraditi
• on će proveriti
• mi ćemo videti

So here, će is the future marker, and proveriti is the infinitive to check / verify.

Because će is a clitic, and clitics in Serbian usually go in the second position of the clause.

So:

• Korisnik će proveriti...

is normal because Korisnik is the first element, and će comes right after it.

If something else came first, će would usually follow that first element:

• Sutra će korisnik proveriti dostupnost.
• Kada bibliotekar stigne, korisnik će proveriti dostupnost.

This second-position behavior is very important in Serbian word order.

Proveriti is the perfective form of the verb, meaning a single completed act: to check / to verify.

In this sentence, the idea is that the user will perform one completed action in the future, so perfective is natural:

• proveriti = to check once, successfully complete the check

If you used an imperfective verb such as proveravati, it would suggest repeated checking, ongoing checking, or a habitual action.

So:

• će proveriti = will check
• će proveravati = will be checking / will check repeatedly

This is a very common point for English speakers.

In Serbian, after conjunctions like kada (when), a future meaning is often expressed with the present tense form of a perfective verb, not with će.

So:

• kada bibliotekar otvori katalog = when the librarian opens the catalog

Even though it refers to the future, Serbian normally says otvori, not će otvoriti, in this kind of subordinate clause.

This is standard and very natural.

Otvori is the 3rd person singular present form of the perfective verb otvoriti.

So:

• otvoriti = to open
• on/ona otvori = he/she opens

In this sentence:

• bibliotekar otvori katalog = the librarian opens the catalog

Even though the form looks like a present tense, because it follows kada and refers to a future event, the whole meaning is future-oriented.

Not quite. Tek kada adds the idea of only when, not until, or only after the moment that.

So the sentence is stronger than plain kada.

Compare:

• kada bibliotekar otvori katalog = when the librarian opens the catalog
• tek kada bibliotekar otvori katalog = only when / not until the librarian opens the catalog

So tek limits the action and emphasizes that the user will check availability only after that condition is met.

Because Serbian often uses a noun where English might use a more flexible expression.

• dostupnost = availability

So:

• proveriti dostupnost = to check availability

This is a fixed and very natural collocation in Serbian.
You are not checking whether something is available in adjective form; you are checking its availability as a noun.

Katalog is in the accusative case because it is the direct object of otvori.

However, for many masculine inanimate nouns, the accusative singular looks exactly the same as the nominative singular.

So:

• nominative: katalog
• accusative: katalog

That is why there is no visible change here.

Dostupnost is also in the accusative case, because it is the direct object of proveriti:

• proveriti šta? → dostupnost

For feminine nouns ending in a consonant, like dostupnost, nominative and accusative singular are often the same in form:

• nominative: dostupnost
• accusative: dostupnost

So again, the case is accusative, even though the word does not visibly change.

Serbian has no articles like English a/an and the.

So:

• korisnik can mean a user or the user
• bibliotekar can mean a librarian or the librarian
• katalog can mean a catalog or the catalog

The exact meaning depends on context.
That is completely normal in Serbian, and learners have to get used to understanding definiteness from the situation rather than from an article.

Yes, absolutely. Serbian word order is flexible, and you can front the time/condition clause for emphasis.

For example:

• Tek kada bibliotekar otvori katalog, korisnik će proveriti dostupnost.

This version may sound even more emphatic, because it highlights the condition first.

Both versions are correct; the difference is mainly in focus and style.

Yes, but it is mostly a matter of style and register.

• kada is the fuller form
• kad is a shorter, very common variant

In everyday speech, both are frequent. In more careful or formal written language, kada may feel slightly more neutral or standard.

So you could also hear:

• Korisnik će proveriti dostupnost tek kad bibliotekar otvori katalog.

The meaning stays the same.

Because the sentence describes two completed, one-time events:

1. the librarian opens the catalog
2. the user checks availability

Perfective verbs fit this very well because they present actions as complete wholes.

• otvoriti → to open (completed action)
• proveriti → to check/verify (completed action)

If imperfective verbs were used instead, the meaning would shift toward process, repetition, or ongoing action.

So the perfective aspect helps show a clear sequence of completed events.