Gledalište je otvoreno.

Not exactly.

Gledalište usually means the auditorium, seating area, viewer area, or spectator section. In some contexts it can also mean the audience side of a theater.

Kazalište is the more general word for theater as a building or institution.

So Gledalište je otvoreno is more like The auditorium / viewing area is open, not necessarily The theater is open in the broadest sense.

Gledalište is neuter singular.

A useful clue is the ending:

• many Croatian nouns ending in -o or -e are neuter
• nouns ending in -ište are very often neuter

That matters because other words that describe the noun must match it in gender and number.

Je is the 3rd person singular present of biti (to be), so it means is.

So the structure is:

gledalište = subject
je = is
otvoreno = open

Very literally: Auditorium is open.

Because otvoreno has to agree with gledalište, which is neuter singular.

Compare:

• otvoren = masculine singular
• otvorena = feminine singular
• otvoreno = neuter singular

So:

• Prozor je otvoren. = The window is open.
• Vrata su otvorena. = The door / doors are open.
• Gledalište je otvoreno. = The auditorium is open.

In this sentence, it behaves like an adjective meaning open.

Historically and grammatically, it comes from a participial form related to the verb otvoriti (to open), but for a learner it is best to read this sentence as:

X je otvoreno = X is open

So here it describes the current state of the auditorium.

It can mean either, depending on context.

In everyday use, je otvoreno often means:

• is open for visitors/customers
• is available / operating

So in a sign or announcement, Gledalište je otvoreno would usually mean the auditorium or seating area is now open for use, not just that a door is standing open.

Croatian normally has no articles like the or a/an.

So gledalište can mean:

• the auditorium
• an auditorium

The exact meaning comes from context. In this sentence, English would usually translate it with the.

Yes, Croatian word order is more flexible than English, but the neutral order here is:

Gledalište je otvoreno.

A different order can change emphasis. For example:

Otvoreno je gledalište.

This is possible, but it sounds more marked, as if emphasizing open or introducing the auditorium later in the sentence.

Also, je is a clitic, so it normally appears in second position in the clause.

In normal standard Croatian, no.

You should say: Gledalište je otvoreno.

Without je, the sentence would sound incomplete in ordinary usage. You may occasionally see omissions in headlines, labels, or very compressed styles, but learners should keep je.

Yes.

It is the subject of the sentence, so it is in the nominative singular:

• gledalište = nominative singular neuter

Because the sentence is simply saying what the auditorium is like, the subject stays in the nominative: Gledalište je otvoreno.