В главном зале работает синхронный перевод.

Because в главном зале expresses location, not motion.

In Russian, в can take:

• the prepositional case for where? → in
• the accusative case for where to? → into

So here:

• в главном зале = in the main hall
• в главный зал = into the main hall

Since the sentence says where the service is operating, Russian uses the prepositional case.

Russian usually uses в for being inside an enclosed space, such as a room, hall, building, or city.

So:

• в зале = in the hall

You would normally not say на зале in standard Russian.
The preposition на is used for things like:

• surfaces: на столе = on the table
• some events/places by convention: на концерте, на работе, на вокзале

With зал, the normal choice for physical location is в.

In Russian, работать is used not only for people who work, but also for services, systems, equipment, offices, websites, hotlines, and facilities.

So работает here means something like:

• is operating
• is functioning
• is available
• is being provided

In this sentence, it does not mean that translation is literally doing a job as a person. It is a natural Russian way to say that the simultaneous interpreting service is running.

In this context, it means simultaneous interpreting.

Russian перевод can refer to both:

• translation in writing
• interpreting in speech

The context tells you which one is meant. The phrase синхронный перевод is the standard term for simultaneous interpretation / simultaneous interpreting at conferences or events.

So even though the literal word is translation, the real meaning here is interpreting.

Because the two adjectives are in different cases.

• главном goes with зале, which comes after в in a location phrase, so it is in the prepositional case
• синхронный goes with перевод, which is the subject of the sentence, so it stays in the nominative case

Forms here:

• главный зал → nominative
• в главном зале → prepositional
• синхронный перевод → nominative

So the endings change because the grammar role changes.

The subject is синхронный перевод.

You can tell because:

• it is in the nominative case
• the verb работает is 3rd person singular
• перевод is a singular noun, so the verb is singular too

So the structure is:

• В главном зале = location
• работает = verb
• синхронный перевод = subject

Even though English often puts the subject first, Russian word order is more flexible.

It is singular because Russian is talking about the service as a whole, not about separate individual translations.

So синхронный перевод here means something like:

• simultaneous interpreting is available
• a simultaneous interpreting service is operating

Russian often uses a singular noun to name a service or type of activity in a general way.

Yes, but the meaning would be slightly different.

• В главном зале есть синхронный перевод = There is simultaneous interpreting in the main hall
• В главном зале работает синхронный перевод = Simultaneous interpreting is operating / being provided in the main hall

So:

• есть focuses on existence
• работает focuses on the service being active and functioning

In announcements, работает often sounds more natural when a service is currently running.

Because Russian has no articles.

Russian does not have separate words for:

• a / an
• the

Whether something is definite or indefinite is understood from:

• context
• word order
• the situation

So в главном зале can mean in the main hall because the context makes it clear which hall is meant.

Yes, Russian word order is flexible, but the emphasis changes.

The given sentence:

• В главном зале работает синхронный перевод

puts the location first, which is very natural in signs and announcements. It sounds like:

• In the main hall, simultaneous interpreting is available

You could also say:

• Синхронный перевод работает в главном зале

This is grammatically possible, but it sounds less like a typical public announcement and gives a different emphasis.

So the original order is natural because it starts with the place where the listener needs to go or pay attention.

Yes. Работает is the present tense imperfective form of работать.

The imperfective is used because the sentence describes:

• an ongoing situation
• a service currently in operation
• a general present-time fact

A perfective verb would not fit well here, because the point is not that the service started or finished, but that it is functioning now.