Želim čestitati baki, jer danas slavi godišnjicu.

Because čestitati takes the dative case for the person you congratulate.

• baka = nominative, the basic dictionary form, meaning grandma
• baki = dative singular, meaning to grandma

So:

• Čestitam baki. = I am congratulating grandma.
• literally, it behaves like I give congratulations to grandma

This is very common in Croatian: some verbs require a specific case, and čestitati is one of the verbs that takes the dative for the recipient.

After želim (I want), Croatian normally uses the infinitive of the second verb.

So:

• želim čestitati = I want to congratulate

This is similar to English want to + verb.

Examples:

• Želim jesti. = I want to eat.
• Želim spavati. = I want to sleep.
• Želim čestitati baki. = I want to congratulate grandma.

So čestitati is in the infinitive because it depends on želim.

Čestitati means to congratulate, but its grammar works a little differently from English.

In English, you usually say:

• congratulate someone

In Croatian, you say:

• čestitati nekome = to congratulate someone
• literally more like to offer congratulations to someone

That is why the person is in the dative:

• Čestitam baki.

You can also add what you are congratulating them for:

• Čestitam baki rođendan. is not the usual way
• more naturally: Čestitam baki rođendan may appear in colloquial usage, but standard Croatian more often uses:
  • Čestitam baki rođendan. / Čestitam baki na rođendanu. Depending on context, native usage varies, but the key beginner point is:
• the person after čestitati is in the dative

Because Croatian often omits subject pronouns when they are clear from the verb form or context.

In this sentence:

• slavi = (he/she) celebrates / is celebrating

The speaker has just mentioned baki, so it is clear that grandma is the one celebrating.

Croatian does this much more often than English. English usually needs the subject:

• because she is celebrating...

Croatian often does not:

• jer danas slavi godišnjicu

If needed for emphasis, you could say:

• jer ona danas slavi godišnjicu

But in normal speech, leaving out ona is more natural.

Because slaviti takes a direct object, and direct objects are usually in the accusative case.

• godišnjica = nominative singular
• godišnjicu = accusative singular

So:

• slavi godišnjicu = she is celebrating an anniversary

This is a standard feminine noun pattern:

• žena → ženu
• knjiga → knjigu
• godišnjica → godišnjicu

Godišnjica means anniversary.

It comes from the idea of something returning yearly:

• godina = year

Depending on context, godišnjica can mean different kinds of anniversaries:

• wedding anniversary
• anniversary of an event
• anniversary of a death
• institutional anniversary, etc.

By itself, slavi godišnjicu usually means is celebrating an anniversary, but the exact type depends on context.

Yes. Jer means because, and it is very common in everyday Croatian.

So:

• Želim čestitati baki, jer danas slavi godišnjicu.
• I want to congratulate grandma, because today she is celebrating an anniversary.

Another common word is zato što:

• Želim čestitati baki zato što danas slavi godišnjicu.

Both are correct. Very generally:

• jer is short and common
• zato što can sound a bit more explicit or emphatic

For a learner, jer is perfectly natural here.

Because jer introduces a subordinate clause explaining the reason.

The sentence has two parts:

• Želim čestitati baki
• jer danas slavi godišnjicu

Croatian normally separates this kind of clause with a comma:

• ..., jer ...

So the comma is standard punctuation here.

Croatian word order is fairly flexible, but some orders sound more natural depending on emphasis.

Here:

• danas slavi godišnjicu = today she is celebrating an anniversary

This sounds neutral and natural. But Croatian could also say:

• jer slavi godišnjicu danas
• jer godišnjicu slavi danas
• jer danas godišnjicu slavi

These alternatives shift the emphasis slightly, and some may sound more literary, marked, or context-dependent.

For learners, the most natural neutral order is usually:

• time expression first: danas
• then verb: slavi
• then object: godišnjicu

Yes, slavi is present tense, 3rd person singular, from slaviti.

• slaviti = to celebrate
• slavi = he/she celebrates / is celebrating

Croatian present tense often covers both:

• simple present
• present continuous

So slavi can mean:

• celebrates
• is celebrating

In this sentence, because of danas (today) and the context, English naturally uses is celebrating.

Želim is 1st person singular present tense.

It means:

• I want

From the verb:

• željeti = to want

A few forms are:

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

As often happens in Croatian, the pronoun ja is omitted because želim already shows who the subject is.

Grammatically, something like that may be understood, but želim is much more natural here.

• želim = I want / I would like
• hoću = I want / I will / I am willing

In many contexts, hoću can sound stronger, more forceful, or more like I insist / I’m going to. For a polite, neutral statement like this, želim čestitati baki is the better choice.

So a learner should treat:

• Želim čestitati baki. as the natural standard version here.

Usually baka means grandma or grandmother, but it can also be used more broadly for an elderly woman, depending on context and tone.

In this sentence, though, the most natural meaning is clearly grandma.

Also note that Croatian family terms are often used very naturally and frequently in everyday speech, so baki here sounds warm and completely normal.

Yes, and that would mean to my own grandma or simply to my grandma, with extra clarity or emphasis.

• Želim čestitati baki. = I want to congratulate grandma.
• Želim čestitati svojoj baki. = I want to congratulate my grandma.

Why is svojoj used?

Because Croatian often uses the possessive svoj when the possessor is the same as the subject.

• svojoj baki = dative singular feminine, matching baki

In many situations, just baki is enough if the relationship is already understood.

It is neutral and natural. It works well in everyday speech and writing.

Nothing in it is especially slangy or especially formal:

• Želim is standard
• čestitati is standard
• jer is common and natural
• slavi godišnjicu is normal standard Croatian

So this is a good model sentence for learners.