Mladoženja kaže da će buket biti spreman čim kuma dođe.

Because mladoženja is a masculine noun with a feminine-looking ending. Croatian has a small group of masculine nouns that end in -a, especially words for male people.

So in this sentence:

• mladoženja = the groom
• it is masculine
• it is in the nominative singular because it is the subject of kaže

Other masculine nouns of this type behave similarly in some cases, even though their ending may look unusual to an English speaker.

Kaže is the 3rd person singular present tense form of kazati or reći, meaning says.

So:

• Mladoženja kaže... = The groom says...

It matches mladoženja, which is singular, so kaže is singular too.

In Croatian, da often introduces a subordinate clause after verbs like say, know, think, hope, and similar verbs.

So:

• kaže da... = says that...

This is very normal Croatian structure. English may optionally leave out that, but Croatian usually keeps da in this kind of sentence.

This is the normal way to express future inside a da-clause.

Breakdown:

• će = future auxiliary
• biti = to be
• spreman = ready

So:

• buket će biti spreman = the bouquet will be ready
• after da, this becomes da će buket biti spreman = that the bouquet will be ready

Croatian does not use an infinitive after say the way English sometimes does. You do not say something like The groom says the bouquet to be ready. Instead, you use a full clause with da.

Because će is a clitic, and Croatian clitics usually go in the second position of their clause.

So in the clause:

• da će buket biti spreman

the clitic će comes right after the first element, which is da.

That is why you get:

• da će buket biti spreman

rather than:

• da buket će biti spreman

Without da, a main clause would normally be:

• Buket će biti spreman.

So the word order changes because of clitic placement.

Because it agrees with buket, which is a masculine singular noun.

Croatian adjectives must agree with the noun they describe in:

• gender
• number
• case

Here:

• buket = masculine singular nominative
• therefore spreman = masculine singular nominative

If the noun were feminine, you would expect spremna. If it were neuter, spremno.

Čim means as soon as.

It introduces a time clause:

• čim kuma dođe = as soon as the kuma arrives / comes

It tells you when the bouquet will be ready.

After time conjunctions like kad, čim, nakon što, and similar words, Croatian often uses the present tense where English uses a future idea.

So Croatian says:

• čim kuma dođe

literally something like:

• as soon as the kuma comes

but the meaning is future:

• as soon as the kuma arrives

This is completely normal. English does something similar too: we say as soon as she arrives, not usually as soon as she will arrive.

The verb here comes from doći, which is a perfective verb meaning to come / arrive as a completed event.

With čim, Croatian usually wants the idea of a completed point in time:

• as soon as she arrives
• not while she is coming

So dođe fits well because it points to the moment of arrival. An imperfective form like dolazi would give a different feel and would usually not be the best choice here.

Kuma is a feminine noun. In wedding contexts, it usually refers to the bride’s female witness or a role similar to maid of honor or wedding sponsor, depending on how closely you want to translate the cultural role.

In Croatian-speaking cultures, kum / kuma can also mean godfather / godmother in other contexts, so the exact English equivalent depends on the situation.

In this sentence:

• kuma is the subject of dođe
• so it is in the nominative singular

Yes. Croatian allows that very naturally.

For example:

• Čim kuma dođe, buket će biti spreman.

This means the same thing. The difference is mostly one of emphasis and sentence flow.

The original version starts with:

• Mladoženja kaže...

so it focuses first on what the groom says.

Yes, buket is a normal Croatian word for bouquet, especially a bouquet of flowers.

In a wedding sentence like this, buket would naturally be understood as the wedding bouquet unless context suggests otherwise.

Yes, and that is a very useful way to understand it.

You can divide it like this:

• Mladoženja kaže = The groom says
• da će buket biti spreman = that the bouquet will be ready
• čim kuma dođe = as soon as the kuma arrives

So the full structure is:

• main clause: Mladoženja kaže
• subordinate content clause: da će buket biti spreman
• time clause inside that idea: čim kuma dođe

That breakdown helps make the grammar much easier to follow.