Demà encara quedaran espelmes i xocolata, però del pastís ja no en voldrà ningú.

Because the sentence talks about tomorrow: Demà.

So Catalan uses the future here:

• quedaran = will remain / will be left
• voldrà = will want

A very literal structure is:

• Demà encara quedaran... = Tomorrow there will still remain...
• ...ja no en voldrà ningú = ...nobody will want any of it anymore

Catalan often uses the future exactly where English does in this kind of sentence.

Here quedar means to remain, to be left over, or to still be there.

So:

• quedaran espelmes i xocolata = there will be candles and chocolate left

This is a very common use of quedar in Catalan and Spanish-like structures:

• Queda pa = There is bread left
• No queda res = There is nothing left

So in this sentence, it is not to meet or to arrange, which are other meanings quedar can have.

Because the subject is actually espelmes i xocolata together.

That is a compound subject, so the verb goes in the plural:

• espelmes = plural
• xocolata = singular
• together: espelmes i xocolata = plural idea overall

So:

• quedaran espelmes i xocolata

This is like English:

• Candles and chocolate will remain, not will remains

Encara here means still.

So:

• Demà encara quedaran espelmes i xocolata
  = Tomorrow there will still be candles and chocolate left

It suggests that even by tomorrow, those things will not have been completely used up.

Common meanings of encara include:

• still
• sometimes even, depending on context

But here still is the natural meaning.

Ja no means no longer or not anymore.

So:

• ja no en voldrà ningú
  = nobody will want any of it anymore = no one will want any more of it

This contrasts nicely with encara:

• encara = still
• ja no = no longer / anymore

So the sentence sets up a contrast:

• some things will still be left
• but cake will no longer be wanted

Del is a contraction of:

• de + el = del

So:

• del pastís = of the cake / from the cake

In this sentence, it has a partitive sense: not necessarily the whole cake, but some of the cake.

That is why the English meaning is often:

• nobody will want any of the cake

So del pastís is not just identifying the cake; it introduces the idea of/from the cake as the source of what someone might want a piece of.

Yes, they are connected, and this is a very important Catalan feature.

En is a clitic pronoun often used for something introduced by de, especially with a partitive meaning:

• voler pastís = to want cake
• voler-ne = to want some of it
• del pastís... en voldrà = of the cake... will want some

So in:

• del pastís ja no en voldrà ningú

the phrase del pastís is brought to the front for emphasis/topic, and en resumes it inside the clause.

A good way to understand it is:

• As for the cake, nobody will want any of it anymore.

This doubling is very natural in Catalan.

Here en is doing the job of of it / some.

With verbs like voler when talking about wanting some quantity of something, Catalan often uses en:

• Vols pastís? = Do you want cake?
• Sí, en vull. = Yes, I want some.
• No en vull. = I don’t want any.

So:

• ja no en voldrà ningú
  literally: nobody will want of-it anymore naturally: nobody will want any anymore

In this sentence, en is the most natural choice because the idea is some of the cake, not the whole cake as a complete object.

Catalan word order is flexible, and ningú often appears after the verb in sentences like this.

So:

• ja no en voldrà ningú

literally looks like:

• already not of-it will-want nobody

but the natural English order is:

• nobody will want any of it anymore

Putting ningú at the end is normal and often gives a smooth, natural rhythm.

You could also see other word orders in Catalan depending on emphasis, but this one is perfectly standard.

Because Catalan uses negative concord.

That means multiple negative-looking words can appear together in the same sentence without canceling each other out.

So:

• no ... ningú = nobody ... not in form, but just nobody in meaning

In Catalan, this is normal:

• No ve ningú = Nobody is coming
• No en voldrà ningú = Nobody will want any

You may also see ningú before the verb, where the pattern can change:

• Ningú no en voldrà is also possible

But with ningú after the verb, no is required.

Because the subject is ningú, which is grammatically singular.

Even though ningú means nobody / no one, Catalan treats it like singular someone/no one:

• ningú voldrà
• not ningú voldran

So:

• ja no en voldrà ningú = no one will want any anymore

This is the same idea as English:

• Nobody wants, not Nobody want

Yes. A more linear version would be something like:

• Demà encara quedaran espelmes i xocolata, però ningú ja no en voldrà del pastís.

But that version sounds less natural. The original:

• Demà encara quedaran espelmes i xocolata, però del pastís ja no en voldrà ningú

is better because del pastís is fronted as the topic or contrastive element.

It is almost like saying:

• As for the cake, nobody will want any of it anymore.

So the original word order helps highlight the contrast:

• candles and chocolate will still be left
• but cake is the thing nobody will want

Yes, and that is exactly why they work so well here.

The sentence contrasts two ideas:

• encara quedaran = will still remain
• ja no en voldrà ningú = already no one will want any / no one will want any anymore

So the speaker is contrasting:

• things that will still be around
• something that will already have lost people’s interest

This kind of contrast is very natural in Catalan:

• encara = persistence
• ja no = end of a previous situation

By itself, xocolata usually means chocolate as a general substance or food, not necessarily one specific bar.

So in this sentence, it probably means some chocolate or chocolate in general among the leftover party food.

That is why the structure is:

• espelmes i xocolata

with:

• espelmes = countable plural
• xocolata = uncountable singular

This is very similar to English:

• candles and chocolate

A very literal gloss would be:

• Demà = tomorrow
• encara = still
• quedaran = will remain / will be left
• espelmes i xocolata = candles and chocolate
• però = but
• del pastís = of the cake
• ja no = no longer / anymore
• en = of it / some
• voldrà = will want
• ningú = nobody

So a very literal English version is:

Tomorrow still will-remain candles and chocolate, but of the cake no longer of-it will-want nobody.

That sounds unnatural in English, of course, but it helps show how the Catalan sentence is built.