Chcemy się wymieniać ubraniami.

Chcemy means we want. It is the 1st-person plural form of chcieć (to want).

In Polish, the verb ending often already shows who the subject is, so a separate word for we is not necessary. You could say My chcemy..., but that adds emphasis, like we do want...

Because Polish uses the infinitive after chcieć, just like English uses to + verb after want.

So the pattern is:

chcemy + infinitive

Examples:

• Chcemy iść = We want to go
• Chcemy czytać = We want to read
• Chcemy się wymieniać ubraniami = We want to swap clothes

Here się makes the action reciprocal: the people involved are doing it with each other.

So wymieniać się ubraniami means to exchange / swap clothes with one another.

This does not always translate neatly as ourselves. In many Polish verbs, się is simply part of how the verb is used.

Because wymieniać się and wymieniać do not mean exactly the same thing.

• wymieniać się czymś = to exchange/swap something with each other
• wymieniać coś can mean to replace something, or in some contexts to mention/list something

So in this sentence, się is important because it gives the idea of a mutual exchange.

Because wymieniać się usually takes the thing exchanged in the instrumental case.

The noun is:

• ubranie = a garment / piece of clothing

Its forms here are:

• ubrania = plural nominative/accusative
• ubraniami = plural instrumental

So:

• wymieniać się ubraniami = to swap clothes

You see the same pattern in:

• wymieniać się książkami = to swap books
• wymieniać się pomysłami = to exchange ideas

This is about aspect, which is very important in Polish.

• wymieniać is imperfective: ongoing, repeated, general, habitual
• wymienić is perfective: one complete exchange

So:

• Chcemy się wymieniać ubraniami suggests a general activity or habit:
  We want to swap clothes
• Chcemy wymienić się ubraniami suggests one specific completed exchange:
  We want to exchange clothes once

Yes, absolutely.

Both are grammatical:

• Chcemy się wymieniać ubraniami
• Chcemy wymieniać się ubraniami

In Polish, się is flexible in position, although it normally does not go at the very beginning of a clause. Many learners will often hear się placed right next to the infinitive, so Chcemy wymieniać się ubraniami may feel slightly more straightforward, but the original sentence is also normal.

In this sentence, it means with each other.

The pattern wymieniać się + instrumental expresses mutual exchange among the people involved.

If you want to say exchange one thing for another, Polish often uses a different structure:

• wymieniać coś na coś
• wymienić dolary na euro = exchange dollars for euros

So wymieniać się ubraniami is about swapping clothes among yourselves, not trading clothes for money or something else.

Yes. Ubrania is a normal, neutral everyday word for clothes.

Some related words are:

• ubrania — neutral, standard
• ciuchy — informal, like clothes / stuff to wear
• odzież — more formal, like clothing / apparel

So ubraniami is a very natural choice in this sentence.

Not usually.

Chcemy się wymieniać ubraniami means We want to swap/exchange clothes with each other.

If you mean change clothes in the sense of putting on different clothes, Polish would more naturally say:

• Chcemy się przebrać
• Chcemy zmienić ubrania

So this sentence is about swapping, not just getting changed.