Ono što mi se u siječnju najviše sviđa jest tišina poslije blagdana.

Ono što is a very common Croatian way to say what in the sense of the thing that or that which.

So:

• ono = that / that thing
• što = which / what / that

Together, ono što literally feels like:

• that which
• the thing that
• what

In this sentence, Ono što mi se u siječnju najviše sviđa... means something like:

• What I like most in January...
• more literally: The thing that pleases me most in January...

This structure is extremely useful in Croatian.

Croatian does not usually express to like the same way English does.

Instead of I like X, Croatian often uses a structure closer to:

• X is pleasing to me

So:

• sviđa se = is pleasing / appeals
• mi = to me

That means:

• sviđa mi se tišina = I like the silence
• literally: The silence pleases me

In your sentence, the subject is the whole idea tišina poslije blagdana, and mi tells us who likes it.

This is why learners often need to mentally flip the sentence:

• English: I like X
• Croatian: X pleases me

In sviđati se / svidjeti se, the se is part of the verb expression. You should learn it together as a unit:

• sviđati se = to be pleasing / to appeal
• svidjeti se = to come to like / to please once, perfective

So in this sentence, se is not optional. You cannot normally say mi sviđa.

Think of the whole pattern as:

• sviđa mi se
• sviđaju mi se

The number changes depending on what is liked, but se stays part of the expression.

u siječnju means in January.

Here u is used with the locative case to express time or location, and siječanj changes to siječnju in the locative singular.

So:

• nominative: siječanj = January
• locative: u siječnju = in January

This is very common with months:

• u siječnju = in January
• u veljači = in February
• u ožujku = in March

So the ending changes because the preposition u here requires the locative.

Yes. najviše here means the most.

It modifies sviđa, so the phrase means:

• mi se najviše sviđa = I like most
• more literally: is most pleasing to me

So:

• Ono što mi se u siječnju najviše sviđa... = What I like most in January...

A useful comparison:

• više = more
• najviše = most

Jest is a fuller, slightly more formal or emphatic form of je (is).

So both of these are possible in many contexts:

• To je dobro.
• To jest dobro.

In your sentence, jest helps clearly connect the first part of the sentence with the predicate:

• Ono što mi se u siječnju najviše sviđa jest tišina poslije blagdana.

It sounds a bit more careful, written, or elegant than je. In everyday speech, many speakers would also say:

• Ono što mi se u siječnju najviše sviđa je tišina poslije blagdana.

Both are correct; jest is just more explicit or formal.

Grammatically, the sentence is structured like this:

• Ono što mi se u siječnju najviše sviđa = the subject-like clause
• jest tišina poslije blagdana = what it is / the complement

So the sentence is basically:

• What I like most in January is the silence after the holidays.

Inside the subordinate clause, the thing being liked is not stated yet. It only appears after jest:

• tišina poslije blagdana

That is why the first half feels incomplete until you reach the end.

Tišina is in the nominative because it functions as the predicate noun after jest.

In other words:

• X jest Y = X is Y

Here:

• Ono što mi se... najviše sviđa = X
• tišina poslije blagdana = Y

Since tišina is the thing identified as what I like most, it stands in the nominative.

Also, if you think of the inner liking structure:

• Tišina mi se sviđa.
• The silence pleases me / I like the silence.

There too, tišina is nominative, because with sviđati se, the thing liked is the grammatical subject.

Poslije means after, and it normally takes the genitive case.

So:

• blagdani = holidays
• after poslije, it becomes blagdana

This is the genitive plural form.

So:

• poslije blagdana = after the holidays

This is a very common pattern:

• poslije ručka = after lunch
• poslije škole = after school
• poslije praznika = after the vacation/holidays

Yes, though they can overlap.

• blagdani usually means holidays/feast days, especially public or religious holidays
• praznici often means vacation, school break, holidays in a broader sense

In this sentence, blagdani fits well because it suggests the holiday period around Christmas and New Year, with all the celebrations. Then tišina poslije blagdana evokes the calm once that festive period is over.

So blagdani is a meaningful choice, not just a random synonym.

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

This sentence is written in a natural and elegant way, but you may hear variations such as:

• Ono što mi se najviše sviđa u siječnju jest tišina poslije blagdana.
• Tišina poslije blagdana jest ono što mi se u siječnju najviše sviđa.

The original version is very natural because it places:

• u siječnju near the idea it modifies
• najviše close to sviđa
• the answer, tišina poslije blagdana, at the end for emphasis

So yes, word order can move, but the original has a nice rhythm and focus.

Short unstressed words in Croatian, called clitics, tend to cluster in a certain position in the sentence. Both mi and se are clitics.

In standard word order, they often appear together early in the clause:

• mi se sviđa
• ti se sviđa
• mu se sviđa

So mi se is the normal order here.

You do not usually say:

• se mi sviđa

The clitic order in Croatian can take some time to get used to, but mi se sviđa is a very common chunk and worth memorizing as a whole.

Because the thing being liked is singular:

• tišina = silence

So the verb agrees with that singular subject:

• Tišina mi se sviđa.

If the thing liked were plural, you would use sviđaju:

• Knjige mi se sviđaju. = I like books.
• literally: Books are pleasing to me.

In your sentence, the hidden subject of the liking is later revealed to be tišina poslije blagdana, which is singular, so sviđa is correct.

You can, but it may sound unnatural in English if you follow it too closely.

A very literal breakdown is:

• Ono = that / that thing
• što = which / that / what
• mi = to me
• se sviđa = is pleasing
• u siječnju = in January
• najviše = most

So, very literally:

• That which is most pleasing to me in January...

Natural English would usually be:

• What I like most in January...

So a word-for-word understanding is useful for grammar, but for translation, it is better to switch into natural English structure.

It is mostly neutral to slightly formal/written, especially because of jest.

Nothing in it is unusual or highly literary, but it sounds a little more polished than casual speech. In everyday conversation, someone might say:

• Najviše mi se u siječnju sviđa tišina poslije blagdana.
• Ono što mi se u siječnju najviše sviđa je tišina poslije blagdana.

The original sentence is very natural in writing and also perfectly understandable in speech, just a bit more carefully phrased.