Sutra idemo u zoološki vrt sa sestrom.

Croatian very often uses the present tense for a future meaning when a future time word is already present, such as sutra (tomorrow).

So Sutra idemo... literally uses present tense, but naturally means We’re going tomorrow or Tomorrow we’re going...

This is similar to English sentences like:

• Tomorrow we’re going to the zoo.
• I’m leaving next week.

You could also express the future with a future-tense form in Croatian, but in everyday speech the present tense is very common in sentences like this.

Sutra means tomorrow and gives the time of the action.

It often appears at the beginning of the sentence because Croatian word order is flexible, and speakers commonly put time expressions early:

• Sutra idemo u zoološki vrt sa sestrom.

But you could also hear:

• Idemo sutra u zoološki vrt sa sestrom.

Putting sutra first gives it a slightly stronger time focus: Tomorrow, we’re going...

This is a very important Croatian pattern:

• u + accusative = motion toward / into a place
• u + locative = location in a place

Here, the sentence means going to the zoo, so it uses movement, which is why we get:

• u zoološki vrt → to the zoo

Compare:

• Idemo u zoološki vrt. = We’re going to the zoo.
• Mi smo u zoološkom vrtu. = We are in the zoo.

So the case changes depending on whether the idea is destination or location.

Yes. Vrt literally means garden, and zoološki vrt literally means zoological garden.

That is simply the normal Croatian expression for zoo.

So:

• zoološki = zoological
• vrt = garden

Together:

• zoološki vrt = zoo

This is a set phrase, so learners should remember it as one vocabulary item.

Because the preposition s / sa meaning with requires the instrumental case.

The noun sestra changes in the instrumental singular to sestrom:

• sestra = sister
• sa sestrom = with (my/your/her) sister

So in this sentence:

• sa sestrom = with sister / with my sister / with the sister

Croatian often leaves out possessives when they are understood from context. English usually needs my sister, but Croatian may simply say sa sestrom.

S and sa are basically the same preposition here. Both can mean with.

Sa is often used for easier pronunciation, especially before certain consonants or consonant clusters. Since sestrom begins with s, sa sestrom sounds smoother than s sestrom.

So:

• sa sestrom is the natural form here.

You may also learn that in some situations both forms are possible, but with words like sestrom, sa is the usual choice.

By itself, sa sestrom literally just means with sister in a grammatical sense, but in natural usage it often means with my sister, with his sister, with her sister, etc., depending on context.

Croatian often omits possessive words when they are obvious.

If you want to be explicit, you can say:

• sa svojom sestrom = with my/one’s own sister
• sa mojom sestrom = with my sister
• sa njegovom sestrom = with his sister

So the original sentence is natural even without a possessive.

Because Croatian has no articles like English a/an/the.

So Croatian simply says:

• u zoološki vrt

Depending on context, English may translate that as:

• to a zoo
• to the zoo

In this sentence, the natural English meaning is usually to the zoo, but Croatian does not mark that difference with an article.

Yes. Croatian word order is more flexible than English word order.

The sentence:

• Sutra idemo u zoološki vrt sa sestrom.

could also appear as:

• Idemo sutra u zoološki vrt sa sestrom.
• Sa sestrom idemo sutra u zoološki vrt.
• U zoološki vrt idemo sutra sa sestrom.

These all keep basically the same core meaning, but the focus changes:

• Sutra... emphasizes when
• Sa sestrom... emphasizes with whom
• U zoološki vrt... emphasizes where

Even though word order is flexible, not every version sounds equally natural in every context. The original sentence is a very normal, neutral way to say it.

Zoološki is an adjective meaning zoological, and it agrees with vrt in:

• gender
• number
• case

Since vrt here is:

• masculine
• singular
• accusative (because of motion after u)

the adjective also appears in the matching form:

• zoološki vrt

This is a basic rule in Croatian: adjectives must match the nouns they describe.

Yes. The ending of the verb already tells you the subject.

Idemo means we go / we are going.

Because Croatian verb endings carry person and number information, the subject pronoun mi (we) is usually unnecessary:

• Idemo. = We’re going.

You can add mi only if you want emphasis:

• Mi idemo sutra... = We are the ones going tomorrow...

So the sentence sounds natural without an explicit subject pronoun.