Ako je lubenica hladna, narezat ćemo je poslije ručka i pojesti vani.

They are two different words that just happen to look the same.

• In Ako je lubenica hladna, je is the verb is.
• In narezat ćemo je, je is the unstressed object pronoun it, referring to lubenica.

So the first je is a form of biti (to be), while the second je is a pronoun.

Because lubenica is a feminine singular noun, and the adjective has to agree with it.

• lubenica = feminine singular
• hladna = feminine singular form of hladan (cold)

So lubenica je hladna means the watermelon is cold, with normal adjective agreement.

This is a standard Croatian future-tense pattern.

The verb is narezati (to slice / cut up), and ćemo is the future auxiliary (we will). When the infinitive comes directly before the future auxiliary, an infinitive ending in -ti usually drops the final -i:

• narezati
  • ćemo
• becomes narezat ćemo

So narezat ćemo means we will slice.

A useful comparison:

• Mi ćemo narezati lubenicu.
• Narezat ćemo lubenicu.

Both are normal, but when the infinitive stands before the auxiliary, you get the shortened form narezat ćemo.

Because Croatian can share them across coordinated verbs.

Here, the sentence means:

• we will slice it after lunch and eat it outside

The future auxiliary ćemo applies to both verbs:

• narezat ćemo ... i pojesti ...

And the object je (it) is understood with the second verb too, even though it is not repeated.

So this is basically:

• narezat ćemo je ... i pojesti (je) vani

Repeating everything would be unnecessary.

Because Croatian is using perfective aspect here.

• rezati = to cut, be cutting, cut in general
• narezati = to cut up / slice up completely
• jesti = to eat, be eating
• pojesti = to eat up / finish eating

In this sentence, the speaker is talking about two completed future actions: first slicing the watermelon, then eating it. That is why the perfective verbs narezati and pojesti are natural here.

Because poslije (after) requires the genitive case.

The noun ručak (lunch) changes in the genitive singular:

• nominative: ručak
• genitive: ručka

So:

• poslije ručka = after lunch

You could also hear nakon ručka, which means the same thing.

Vani is an adverb meaning outside or outdoors.

So pojesti vani means:

• eat outside
• eat outdoors

It is not a noun, so there is no case ending to worry about here.

Because Croatian normally uses the present tense after ako for a real, open condition.

So Ako je lubenica hladna means If the watermelon is cold. This is very similar to English, which also says if it is cold, not normally if it will be cold.

In other words, Croatian is not doing anything strange here: it is simply stating the condition first, and then the future result in the main clause.

Yes, Croatian word order is fairly flexible, but not completely free.

This sentence is very natural as written:

• Ako je lubenica hladna, narezat ćemo je poslije ručka i pojesti vani.

But you could also say, for example:

• Ako je lubenica hladna, poslije ručka ćemo je narezati i pojesti vani.

The main thing to remember is that short unstressed words like ćemo and je follow special placement rules, so they cannot just go anywhere.

Because Croatian has no articles.

So lubenica can mean:

• a watermelon
• the watermelon

and the context tells you which one is meant.

The same is true for ručak:

• lunch
• the lunch

Croatian relies on context, word order, and the situation instead of using articles like English does.