Després de la festa, encara queden sis globus a la sala.

Because in Catalan, després normally takes de when it is followed by a noun or noun phrase.

• després de la festa = after the party
• després de dinar = after lunch

If després appears on its own, it usually means later / afterwards:

• Ho farem després. = We’ll do it later.

So here de is required because la festa comes after it.

Because festa is a feminine singular noun, so it takes the article la.

• de + el = del
• de + la = de la

So:

• després del concert
• després de la festa

There is no contraction with la here.

Encara means still here.

It gives the idea that, even after the party is over, the balloons have not all gone away. So it adds a sense of continuation or persistence.

Compare:

• Queden sis globus a la sala. = Six balloons remain in the room.
• Encara queden sis globus a la sala. = There are still six balloons left in the room.

So encara makes the sentence feel more like surprisingly / even now / still.

Because the subject is sis globus, which is plural.

With quedar meaning to remain / be left, the verb agrees with the thing that remains:

• Queda un globus. = One balloon remains.
• Queden sis globus. = Six balloons remain.

So queden is plural to match sis globus.

Catalan often leaves out subject pronouns when they are not needed. This is very normal.

The verb ending already tells you important information, and in this sentence the noun sis globus makes the subject clear anyway. So adding a pronoun would be unnecessary.

Catalan does this much more than English:

• Queden sis globus.
• not usually Ells queden sis globus.

In fact, a pronoun there would sound odd.

Because quedar gives the idea of remaining or being left, which fits the context of after the party.

• Hi ha sis globus a la sala. = There are six balloons in the room.
• Encara queden sis globus a la sala. = There are still six balloons left in the room.

So hi ha is more neutral: it just says something exists somewhere.
Queden is more specific: it says those balloons are what remains.

Yes, it is plural here.

Globus is one of the Catalan nouns whose singular and plural forms can look the same. The number is shown by the article, the verb, or a number word:

• un globus
• sis globus
• els globus

So in this sentence, sis and queden make it clear that globus is plural.

Catalan often uses a where English uses in or at.

So a la sala is a perfectly normal way to say in the room.

Depending on the variety of Catalan and the context, en can also appear in some location expressions, but a la sala is very natural and standard here.

So do not translate prepositions too literally from English:

• English: in the room
• Catalan: a la sala

Yes, Catalan word order is fairly flexible, but this version is very natural.

The sentence begins with a time phrase:

• Després de la festa

Then comes encara, then the verb, then the subject, then the place:

• encara queden sis globus a la sala

Other orders are possible for emphasis, for example:

• A la sala encara queden sis globus.

But the original order is a very normal, neutral way to say it.

The comma separates the introductory time phrase from the main clause.

• Després de la festa, = introductory setting
• encara queden sis globus a la sala. = main statement

In Catalan, this comma is very common and helps readability, especially when the opening phrase is more than just one short word. In some short sentences, writers may omit such a comma, but here it is very natural.

Because the location is already expressed directly as a la sala, so no locative pronoun is needed.

Catalan can use hi to refer back to a place that has already been mentioned, for example:

• A la sala, encara hi queden sis globus.

Here hi refers back to a la sala.

But in the original sentence, the full location phrase is already present, so hi is not necessary:

• Després de la festa, encara queden sis globus a la sala.

That is completely normal.