Mesnica u susjednoj ulici je otvorena rano.

Mesnica means butcher’s shop or butcher’s.

Grammatically, it is:

• a feminine noun
• singular
• in the nominative case here, because it is the subject of the sentence

That is why other words in the sentence match it as feminine singular.

Because otvorena has to agree with mesnica.

In Croatian, adjectives and adjective-like forms agree with the noun in:

• gender
• number
• sometimes case

Since mesnica is feminine singular, the form is:

• masculine: otvoren
• feminine: otvorena
• neuter: otvoreno

So mesnica je otvorena = the butcher’s shop is open.

Because this phrase means in/on the neighboring street, and after u when talking about a location, Croatian uses the locative case.

The base forms are:

• susjedna = neighboring
• ulica = street

But in the locative singular they become:

• susjednoj
• ulici

So:

• susjedna ulica = a neighboring street
• u susjednoj ulici = in/on the neighboring street

Both the adjective and the noun change, because they must match in case, gender, and number.

Yes. U can take either locative or accusative, depending on meaning.

• u + locative = location, being somewhere
• u + accusative = motion into somewhere

Here the butcher’s shop is already located there, so Croatian uses locative:

• u susjednoj ulici = in/on the neighboring street

Compare:

• Mesnica je u susjednoj ulici. = The butcher’s shop is in the neighboring street.
• Idem u susjednu ulicu. = I’m going into/to the neighboring street.

So the case changes with the idea of location vs movement.

In this sentence, je otvorena means is open.

That can be confusing, because Croatian uses a form that looks like a past passive participle:

• otvoren / otvorena / otvoreno

So depending on context, je otvorena can sometimes look like:

• is open = a state
• was opened / has been opened = a passive idea

Here, the natural reading is the state:

• Mesnica ... je otvorena rano. = The butcher’s shop ... is open early.

A native speaker understands this from context.

Rano is an adverb, meaning early.

It describes when the shop is open.

• otvorena rano = open early

It is not rana, because rana would be an adjective form, not an adverb.

Compare:

• rana jutra type adjective use = early mornings
• rano otvara or je otvorena rano = opens early / is open early

A useful pattern is:

• adjective: ran = early
• adverb: rano = early

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

Very importantly, that means second position after the first whole phrase, not necessarily after the first single word.

In this sentence, the first phrase is:

• Mesnica u susjednoj ulici

Then comes the clitic:

• je

So:

• Mesnica u susjednoj ulici je otvorena rano.

This is normal Croatian word order.

Yes, Croatian word order is more flexible than English word order.

For example, you may also hear:

• Mesnica u susjednoj ulici rano je otvorena.

That still means the same thing, but the emphasis shifts slightly.

However, not every rearrangement sounds equally natural, and clitics like je still have to follow the usual placement rules. So for a learner, the given sentence is a good neutral model to copy.

Because prepositions do not match one-to-one across languages.

Croatian often uses u where English uses:

• in
• on
• sometimes at

So:

• u ulici literally looks like in the street, but in natural English the best translation may be on the street or in the street, depending on context.

This is normal and just has to be learned as Croatian usage:

• u ulici
• u gradu
• u školi

So do not translate the preposition too literally every time.

Yes.

• susjed = neighbor
• susjedna / susjedni = neighboring, adjacent

So susjednoj ulici means the neighboring street or the adjacent street.

This is a common Croatian way to describe something nearby:

• u susjednoj zgradi = in the neighboring building
• u susjednom selu = in the neighboring village

So if you know susjed, the adjective susjedni / susjedna / susjedno is a useful related word to learn.