La faldilla vermella és la que vol portar la meva filla a la festa.

Because vermella has to agree with faldilla, which is feminine singular.

• vermell = masculine singular
• vermella = feminine singular
• vermells = masculine plural
• vermelles = feminine plural

So:

• la faldilla vermella
• el vestit vermell

Here la que means the one that / the one which.

It refers back to la faldilla vermella. So the sentence is identifying the skirt:

• La faldilla vermella és la que...
• The red skirt is the one that...

In this structure, la works like the one, and que introduces the clause that explains which one.

The two las are doing different jobs.

1. La faldilla: this la is the normal definite article, meaning the.
2. la que: this la stands for the one.

So it is not just repetition for no reason. The second la is part of the identifying structure la que...

This structure puts emphasis on which skirt it is.

It is more specifically identifying the item than a simpler sentence like:

• La meva filla vol portar la faldilla vermella a la festa.

That simpler version means My daughter wants to wear the red skirt to the party.

But the original sentence means something more like:

• The red skirt is the one my daughter wants to wear to the party.

So the focus is on the red skirt.

The subject is la meva filla.

Even though it comes after the verbs, it is still the person doing the wanting and the wearing:

• vol = wants
• portar = to wear
• la meva filla = my daughter

Catalan often allows the subject to come after the verb, especially in relative clauses like this one.

So:

• la que vol portar la meva filla = the one my daughter wants to wear

Because this is a very common verb pattern, just like in English:

• vol = wants
• portar = to wear

So:

• vol portar = wants to wear

The first verb is conjugated (vol, from voler), and the second stays in the infinitive (portar).

Yes. With clothes, portar commonly means to wear.

Catalan portar has a broader range than English wear. Depending on context, it can mean things like:

• to carry
• to bring
• to take
• to wear

In this sentence, because the object is a skirt, the meaning is clearly to wear.

In Catalan, possessives are usually used with the definite article:

• la meva filla = my daughter
• el meu llibre = my book
• la nostra casa = our house

That is different from English, where we do not use the with possessives.

So Catalan says:

• la meva filla

not normally:

• meva filla

a la festa means to the party or, depending on context, for the party / at the party.

The preposition a is very common for places, destinations, and events. Here it tells you the occasion connected to the wearing:

• portar ... a la festa = wear ... to the party

So the idea is that this is the skirt she wants to wear for that event.

The accent in és helps distinguish it from es.

• és = is (from ser)
• es = a pronoun, as in reflexive constructions

So in this sentence:

• és = is

The accent also shows the stressed vowel. This is a very common word, so it is worth learning as a fixed form.

Yes, absolutely. That version is also natural.

These two are both correct:

• La faldilla vermella és la que vol portar la meva filla a la festa.
• La faldilla vermella és la que la meva filla vol portar a la festa.

The difference is mostly one of word order and style. The second may feel clearer to many learners because the subject la meva filla comes before the verb phrase in the relative clause. The original version is also perfectly good Catalan.