Prodavačica nas šalje do vage, jer paprike i krastavce moramo staviti na vagu prije nego što dođemo do blagajne.

Prodavačica means female shop assistant / saleswoman. Croatian often marks natural gender in profession words:

• prodavač = male shop assistant / salesman
• prodavačica = female shop assistant / saleswoman

So this sentence tells you the person is female.

Mi means we, which is a subject form.

Nas means us, which is an object form. In this sentence, the shop assistant is sending us, so Croatian uses nas.

It also appears right after Prodavačica because nas is an unstressed pronoun, and these pronouns usually go in the second position in the sentence or clause.

So:

• Prodavačica nas šalje... = natural
• Prodavačica šalje nas... = possible only with special emphasis

Because do requires the genitive case.

The dictionary form is vaga = scale.
After do, it becomes vage:

• vaga
• do vage

Here do means something like to, up to, or over to. So šalje do vage means sends us to the scale.

These are the forms used because the vegetables are the direct objects of staviti.

Dictionary forms:

• paprika = pepper
• krastavac = cucumber

In this sentence, they appear in the accusative plural:

• paprike
• krastavce

So the sentence is talking about putting the peppers and cucumbers onto the scale.

A useful point: different nouns can have different accusative plural endings, so paprike and krastavce do not need to look alike.

Croatian uses a modal verb + infinitive structure:

• moramo = we must / we have to
• staviti = put

So:

• moramo staviti = we must put

Unlike English, Croatian does not use a separate word like to before the infinitive here.

This is a question of aspect.

• staviti = perfective → to put, as a completed action
• stavljati = imperfective → to be putting, to put repeatedly/habitually

Here the meaning is that the vegetables need to be put on the scale as a single completed step before going to the checkout, so staviti is the natural choice.

Because Croatian uses different cases depending on whether there is movement or location.

• na vagu = onto the scale / to the scale
  na + accusative for movement
• na vagi = on the scale
  na + locative for location

In this sentence, the vegetables are being placed onto the scale, so na vagu is correct.

Prije nego što means before when it introduces a whole clause.

So:

• prije nego što dođemo do blagajne = before we get to the checkout

This is a very common and standard structure.

You may also hear prije nego dođemo, without što, but prije nego što is extremely common and very natural.

A helpful contrast:

• prije nego što + clause
• prije + noun/genitive

For example:

• prije nego što dođemo... = before we come/get...
• prije blagajne = before the checkout

In Croatian, after conjunctions like prije nego što, it is very common to use the present tense form even when the meaning is future.

Here:

• dođemo = present form of doći
• but in context it means before we get / before we come / before we reach

So Croatian does not need something like before we will come. The present form is the normal choice here.

Again, do takes the genitive case.

The dictionary form is:

• blagajna = checkout, cash register, till

After do, it becomes:

• blagajne

So:

• do blagajne = to the checkout / up to the checkout

In the phrase dođemo do blagajne, the whole expression means we get to / we reach the checkout.

No, Croatian word order is fairly flexible.

The given sentence says:

• paprike i krastavce moramo staviti na vagu

But you could also say:

• moramo staviti paprike i krastavce na vagu

Both are grammatical.

The version in your sentence gives a little more prominence to paprike i krastavce. Croatian often moves parts of the sentence around for emphasis, rhythm, or information structure.

The main exception is that short unstressed words like nas have much stricter placement rules, which is why nas stays near the beginning.