Žao mi je što sam zaboravila sandale, pa ću morati hodati u tenisicama.

Yes, Žao mi je is a very common fixed expression meaning I’m sorry or I regret it.

Literally, it works more like It is regretful to me than like the English verb I am sorry. Its parts are:

• žao = sorry/regretful
• mi = to me
• je = is

So Croatian expresses this idea as a state that affects the speaker, not as a normal verb like English does.

You will also see:

• Žao mi je zbog toga. = I’m sorry about that.
• Žao mi je što kasnim. = I’m sorry that I’m late.

Mi is the dative form of ja and means to me.

In Croatian, a lot of feelings and physical states are expressed with the person in the dative, especially in expressions like:

• Drago mi je. = I’m glad.
• Hladno mi je. = I’m cold.
• Žao mi je. = I’m sorry.

So mi is there because Croatian treats this as something that is emotionally felt by me / to me.

Here što introduces the reason or content of the regret: that / the fact that.

So:

• Žao mi je što sam zaboravila sandale. = I’m sorry that I forgot the sandals.

In this kind of sentence, što is very common after expressions like žao mi je, drago mi je, krivo mi je, etc.

Croatian past tense usually needs two parts:

• the present form of biti as an auxiliary
• the past participle of the main verb

So:

• sam = auxiliary for I
• zaboravila = past participle of zaboraviti

Together, sam zaboravila means I forgot.

Croatian often drops the subject pronoun ja, because sam already shows the person.

Because the speaker is female.

In Croatian past tense, the participle agrees with the gender of the speaker:

• zaboravila = a woman is speaking
• zaboravio = a man is speaking

So this sentence specifically sounds as if it is said by a female speaker.

Sandale is the direct object of zaboravila, so it is in the accusative plural.

For this noun, the nominative plural and accusative plural have the same form:

• nominative plural: sandale
• accusative plural: sandale

So even though the form looks the same, the function here is accusative because it is the thing that was forgotten.

Here pa means something like so, and so, or therefore.

It connects the first idea to the consequence:

• I forgot the sandals, so I’ll have to walk in sneakers.

It is very common in everyday Croatian and often sounds natural and conversational.

This is the future tense.

• ću = I will
• morati = have to

So ću morati means I will have to.

The clitic ću comes early in the clause, which is normal in Croatian. After pa, it naturally appears as:

• pa ću morati...

A more expanded version would be:

• pa ja ću morati...

But ja is usually omitted.

Hodati means to walk and is the natural verb here for the activity that follows.

It is an imperfective verb, which fits well because the meaning is not about one completed act, but about the general activity of walking.

So:

• morati hodati = to have to walk

This sounds normal and idiomatic in Croatian.

After u, this is the locative plural, and it means in sneakers / wearing sneakers.

So:

• u tenisicama = in sneakers, with sneakers on

This is a very common Croatian way to talk about what someone is wearing:

• u kaputu = in a coat
• u haljini = in a dress
• u cipelama = in shoes

For tenisice, the plural ending -ama is used in the dative, locative, and instrumental plural, but after the preposition u, the case is locative.

Literally, yes, but idiomatically it simply means wearing sneakers.

English usually says in sneakers or wearing sneakers, and Croatian uses u + locative very naturally for clothing and footwear.

So in this sentence, hodati u tenisicama just means to walk in sneakers.

Yes, some parts could move, but the given version is very natural.

For example:

• Žao mi je što sam zaboravila sandale, pa ću morati hodati u tenisicama.

is normal and smooth.

You could also hear:

• Žao mi je što sam sandale zaboravila...

but that sounds more marked or emphasized.

Croatian word order is flexible, but clitics such as mi, je, sam, and ću tend to stay near the beginning of their clause, which is why the sentence is arranged this way.