Abans de pagar, vull tornar a veure la faldilla al provador.

It is a time expression meaning before paying. Putting it at the beginning sets the scene first: Before paying, I want...

This is very natural in Catalan, just as it is in English. You could also say:

Vull tornar a veure la faldilla al provador abans de pagar.

That would also be correct, but the original version gives a little more emphasis to the timing.

Abans de means before when it is followed by a verb in the infinitive.

So:

• abans de pagar = before paying
• abans de marxar = before leaving
• abans de comprar-ho = before buying it

The de is required in this structure in Catalan.

Because after abans de, Catalan uses the infinitive.

So the pattern is:

• abans de + infinitive

Examples:

• abans de menjar = before eating
• abans de sortir = before going out
• abans de pagar = before paying

This works much like English before + -ing or before + clause, but Catalan prefers the infinitive here.

Vull is the 1st person singular present of voler = to want.

So:

• vull = I want

A few forms of voler are:

• vull = I want
• vols = you want
• vol = he/she/it wants

In the sentence, vull tells you the subject is I, so Catalan does not need to say jo.

Catalan often leaves out subject pronouns because the verb ending already shows who the subject is.

So:

• vull already means I want
• jo vull is possible, but only if you want extra emphasis or contrast

For example:

• Jo vull veure-la, però ella no.
  I want to see it, but she doesn’t.

In your sentence, jo would be unnecessary.

This is a very common Catalan structure:

• tornar a + infinitive = to do something again

So:

• tornar a veure = to see again
• tornar a provar = to try again
• tornar a venir = to come again

Literally, tornar by itself can mean to return, but in this pattern it works like again.

So vull tornar a veure la faldilla means I want to see the skirt again, not I want to return to see the skirt.

Because the sentence contains two linked verb structures:

1. vull + infinitive
   vull tornar... = I want to go back / I want to again...

2. tornar a + infinitive
   tornar a veure = to see again

So the full chain is:

• vull = I want
• tornar a veure = to see again

Together:

• vull tornar a veure = I want to see again

This kind of stacking is very normal in Catalan.

Because Catalan normally uses the definite article with a specific noun that both speaker and listener can identify.

So:

• la faldilla = the skirt

In this context, it means a particular skirt already known in the conversation, probably one the speaker has already tried on or looked at.

Using faldilla without the article here would sound unnatural.

Al is the contraction of:

• a + el = al

So:

• al provador = to the fitting room / at the fitting room / in the fitting room, depending on context

This contraction is mandatory in standard Catalan when a is followed by el.

Similarly:

• de + el = del

In Catalan, a can express more than just movement toward a place. Depending on context, it can also correspond to English at or sometimes in.

So al provador here is naturally understood as the location where the speaker wants to see the skirt again: in the fitting room.

This is something you often have to learn as a usage pattern rather than translate word for word.

Here provador means fitting room or changing room in a clothes shop.

So:

• al provador = in the fitting room

In other contexts, words from the same root can relate to trying or testing, but in a clothing-shopping sentence, provador is clearly the place where you try clothes on.

Yes. If the skirt has already been mentioned, Catalan could replace la faldilla with a pronoun.

For example:

• Abans de pagar, la vull tornar a veure al provador.
  Before paying, I want to see it again in the fitting room.

Here la stands for the skirt.

In your original sentence, the full noun la faldilla is used for clarity.