Za rođendan želi malu tortu sa čokoladom.

Serbian often omits subject pronouns when they are already clear from the verb form or from context. This is called a pro-drop language.

Here, želi is 3rd person singular, so it means he/she wants. The sentence itself does not tell you whether the person is male or female; context does.

Želi is the present tense, 3rd person singular form of želeti (to want).

So:

• ja želim = I want
• ti želiš = you want
• on/ona želi = he/she wants

In this sentence, želi matches an understood subject like he or she.

Serbian word order is fairly flexible. Putting Za rođendan first gives the occasion/background first: for the birthday / for a birthday.

That sounds natural in Serbian, especially when the speaker wants to set the scene first.

You could also say: Želi malu tortu sa čokoladom za rođendan.

That is also understandable, but the emphasis shifts slightly.

After za in this meaning, Serbian uses the accusative case.

Rođendan is a masculine inanimate noun. For many masculine inanimate nouns, the nominative and accusative singular look the same.

So:

• nominative: rođendan
• accusative: rođendan

That is why you see za rođendan, not a visibly different form.

Because malu tortu is the direct object of želi, and direct objects usually go into the accusative case.

The basic dictionary forms are:

• mala = small
• torta = cake

In the feminine singular accusative, they become:

• malu
• tortu

So:

• nominative: mala torta
• accusative: malu tortu

The adjective must agree with the noun in gender, number, and case.

After sa (with), Serbian normally uses the instrumental case.

The noun is:

• nominative: čokolada
• instrumental singular: čokoladom

So:

• sa čokoladom = with chocolate

This is a very common pattern:

• sa sirom = with cheese
• sa voćem = with fruit
• sa kremom = with cream

Not exactly.

• čokoladna torta usually means a chocolate cake as a type
• torta sa čokoladom means a cake with chocolate

The second one can suggest chocolate as an ingredient, filling, topping, or accompaniment. In real life, the meanings can overlap, but grammatically they are not identical.

Also compare:

• torta od čokolade = a cake made of chocolate / a cake of chocolate

So Serbian has several ways to express related ideas, with slightly different nuances.

You do not know from this sentence alone. Serbian often leaves that kind of information to context.

Za rođendan can simply mean:

• for a birthday
• for the birthday occasion
• for his/her birthday, if context already makes that clear

If Serbian wants to be specific, it can say:

• za njen rođendan = for her birthday
• za njegov rođendan = for his birthday
• za moj rođendan = for my birthday

Because Serbian has no articles.

So malu tortu can mean:

• a small cake
• the small cake

Context tells you which is meant.

If Serbian wants to make something feel more like a/an, it may use jedan/jednu in some situations:

• jednu malu tortu = one / a small cake

But that is not required the way English requires a or the.

Yes. In the present tense, Serbian verb forms usually do not show the gender of the subject.

So želi can mean:

• he wants
• she wants

You only learn the gender from:

• context
• a pronoun like on or ona
• or some other clue in the conversation

Yes. It is a perfectly normal Serbian sentence.

It has:

• an occasion phrase: Za rođendan
• a verb: želi
• a direct object: malu tortu
• an additional phrase describing the cake: sa čokoladom

The only thing left unstated is the subject and whose birthday it is, but Serbian often leaves those implied when they are already understood.