Sutra želim da idem u park.

In Serbian, after verbs like želeti (to want), it is very common to use:

• da
  • present-tense verb

So želim da idem is the normal Serbian way to say I want to go.

Even though ići is the infinitive (to go), Serbian usually prefers želim da idem over želim ići. The infinitive is much less common in standard everyday Serbian than it is in some neighboring languages, especially Croatian.

Because after da, Serbian normally uses a present-tense form, even when the meaning is future.

Here:

• želim = I want
• da idem = literally something like that I go, but naturally to go
• sutra tells you the action is in the future

So the future meaning comes from the whole sentence, especially sutra, not from the form idem by itself.

Da introduces a subordinate clause. In sentences like this, it often works like the English to in to go, although it is not a true infinitive marker.

So:

• želim da idem = I want to go

A useful beginner pattern is:

• želim da... = I want to...
• moram da... = I have to...
• mogu da... = I can...

So da is a very important linking word in Serbian grammar.

Because Serbian often drops subject pronouns when they are already clear from the verb ending.

Here, želim already means I want, so ja is not necessary.

You could say:

• Ja želim da idem u park.

But that sounds more emphatic, like:

• I want to go to the park.

In neutral sentences, leaving out ja is completely normal.

This is about case and movement.

With u, Serbian uses:

• accusative for motion into/to
• locative for location in/at

So:

• Idem u park. = I am going to the park.
  
  • movement
  • park is accusative

But:

• Ja sam u parku. = I am in the park.
  
  • location
  • parku is locative

Since this sentence is about going somewhere, u park is correct.

Because park is a masculine inanimate noun, and in the singular its accusative form is the same as its nominative form.

So:

• nominative: park
• accusative: park

That is why you do not see a change here, even though the case has changed.

You do see a difference in the locative:

• u parku = in the park

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

The sentence:

• Sutra želim da idem u park.

is natural and puts sutra first, which makes the time frame prominent.

You could also hear:

• Želim da idem u park sutra.
• Želim sutra da idem u park.

These all mean roughly the same thing, but the emphasis shifts slightly.

For a learner, the original sentence is a very good neutral pattern.

Yes, but the tone is a little different.

• Želim da idem u park. = I want to go to the park.
• Hoću da idem u park. = also I want to go to the park, but often sounds more direct, stronger, or more conversational

Želim can sound a bit more polite, thoughtful, or formal than hoću.

So both are possible, but they are not always identical in tone.

They are similar, but not exactly the same.

• Sutra želim da idem u park. = Tomorrow I want to go to the park.
  This expresses a desire or intention.

• Sutra ću ići u park. = Tomorrow I will go to the park.
  This is a straightforward future statement or plan.

So želim da idem focuses on what the speaker wants, while ću ići focuses on the future action itself.

Because Serbian does not have articles like English a and the.

So park can mean:

• a park
• the park

The exact meaning depends on context.

In this sentence, English would usually translate it as the park, but Serbian does not need a separate word for that.

Ići is perfectly natural here.

• ići = to go in a general sense
• otići = to leave / to go away / to go off, often more focused on a completed departure

So:

• želim da idem u park = neutral and very natural
• želim da odem u park = also possible, but it can sound a bit more like I want to go over to the park / make the trip there

At a beginner level, idem u park is the safest and most common choice.

No. In a simple sentence like this, you normally do not put a comma after Sutra.

So the correct punctuation is:

• Sutra želim da idem u park.

A comma would usually only appear if there were some extra clause or parenthetical element.