Iako je vani hladno, nećakinja želi ići na ljuljačku.

Iako means although / even though. It introduces a subordinate clause that gives a contrast to the main idea.

• Iako je vani hladno = Although it is cold outside
• nećakinja želi ići na ljuljačku = the niece wants to go on/to the swing

So the sentence sets up a contrast: it is cold, but she still wants to go.

Because iako je vani hladno is a subordinate clause introduced by iako. In Croatian, subordinate clauses are normally separated by a comma from the main clause.

So:

• Iako je vani hladno, nećakinja želi ići na ljuljačku.

You could also reverse the order:

• Nećakinja želi ići na ljuljačku, iako je vani hladno.

The comma is still used.

Croatian often uses an impersonal construction for weather and general conditions.

• hladno je = it is cold
• vruće je = it is hot
• mračno je = it is dark

English needs the dummy subject it, but Croatian does not. So je hladno literally looks like is cold, but it naturally means it is cold.

Yes. Vani means outside / outdoors.

In this sentence:

• vani je hladno = it is cold outside

It is a very common everyday word. Depending on region and style, you may also hear napolju, but vani is extremely common and natural.

Yes. Nećakinja means niece, so it refers specifically to a female relative.

Related words:

• nećak = nephew
• nećakinja = niece

It is a feminine noun.

This is the normal Croatian pattern for want + infinitive.

• željeti = to want
• želi = he/she wants
• ići = to go

So:

• želi ići = wants to go

Croatian does not need a separate word for to before the second verb in this kind of structure. The infinitive ići already carries that meaning.

Because after želi (wants), Croatian normally uses an infinitive to express the action that someone wants to do.

Compare:

• Želim spavati. = I want to sleep.
• Želi jesti. = He/She wants to eat.
• Nećakinja želi ići. = The niece wants to go.

So ići stays in the base infinitive form, not a conjugated form like ide.

Croatian uses different prepositions depending on the kind of movement.

• na often means movement onto a surface or toward something conceived as a place/activity
• u usually means movement into something

A ljuljačka is a swing, so Croatian naturally says:

• ići na ljuljačku = to go on/to the swing

That is the idiomatic expression. Using u ljuljačku would sound wrong here.

Because after na expressing movement, Croatian usually uses the accusative case.

The noun ljuljačka is feminine, and its forms are:

• nominative singular: ljuljačka
• accusative singular: ljuljačku

So:

• na ljuljačku = to the swing / onto the swing

This case change shows direction or motion toward a goal.

Yes, depending on context, it can suggest either:

• going to the swing
• going on the swing

In everyday speech, ići na ljuljačku often means going to use the swing, so English may translate it a bit differently depending on the situation.

Because Croatian has no articles. There is no direct equivalent of English a/an/the.

So:

• nećakinja can mean a niece or the niece
• ljuljačku can mean a swing or the swing

Context tells you which one is meant. In this sentence, English would usually choose the niece or just the niece/niece depending on the wider context.

Yes. Croatian word order is more flexible than English word order, although not completely free.

For example, you can say:

• Iako je vani hladno, nećakinja želi ići na ljuljačku.
• Nećakinja želi ići na ljuljačku iako je vani hladno.

Both are natural. The first version puts more emphasis on the contrast right away: Although it is cold outside...

Yes. Croatian clitic forms like je often tend to appear in the second position of their clause.

In:

• Iako je vani hladno

the conjunction iako comes first, and the clitic je follows early in the clause.

You will often notice this with short forms such as:

• je
• sam
• si
• se
• ga
• mu

This is a very important Croatian word-order pattern.

These are good words to pay attention to because they contain sounds English speakers often find difficult.

A rough guide:

• nećakinja ≈ neh-cha-kin-ya, but with ć being a softer sound than English ch
• ljuljačku ≈ lyool-yach-koo, with lj sounding like the lli in some pronunciations of million

Useful notes:

• ć is softer than č
• lj is a single Croatian sound, not just l + j
• nj in nećakinja is also a single sound, similar to ny in canyon

Exact pronunciation takes practice, but those approximations can help you get started.