Avui no podem pujar a la muntanya perquè plou, però demà volem fer l'excursió.

Catalan often leaves out subject pronouns when the verb form already makes the subject clear.

• podem = we can
• volem = we want

So nosaltres is not necessary here. You could say Avui nosaltres no podem... or Demà nosaltres volem..., but that would usually add emphasis or contrast, not just state the basic idea.

They are both 1st person plural present indicative forms:

• podem ← poder = to be able to / can
• volem ← voler = to want

So:

• no podem pujar = we can’t go up / we can’t climb
• volem fer = we want to do / we want to go on

In Catalan, the normal negation pattern is simply:

• no + conjugated verb

So:

• no podem = we cannot / we can’t
• no plou = it isn’t raining

Unlike English, Catalan does not need a helper like do. You do not say something equivalent to we do not can.

Literally, it means to go up to the mountain or to climb/go up the mountain.

A few useful points:

• pujar usually involves an idea of going upward
• a la muntanya means to the mountain

Depending on context, a natural English translation could be:

• go up the mountain
• go to the mountain
• head up into the mountains

If the speaker just meant go to the mountains with no idea of upward movement, Catalan might also use anar a la muntanya in other contexts.

Catalan normally uses an article where English sometimes would not.

So:

• la muntanya = the mountain

In this sentence, the mountain is treated as a known or identifiable place. Catalan often sounds more natural with the article here than bare muntanya would.

Here, perquè means because:

• ...perquè plou = ...because it’s raining

This is different from per què, which usually means why or for what:

• Per què plou? = Why is it raining?

So the accent and the spacing matter:

• perquè = because
• per què = why / for what

Because weather verbs in Catalan are usually impersonal.

• plou = it’s raining
• neva = it’s snowing

English needs a dummy subject, it, but Catalan does not. So plou is a complete sentence by itself. You would not normally say ell plou.

Però means but, and it is written with an accent on ò.

The accent helps show the correct stress and vowel quality. It also distinguishes it clearly from other similar-looking combinations involving per.

So in this sentence:

• ..., però demà... = ..., but tomorrow...

Because però introduces a contrasting clause, and Catalan normally separates that with a comma:

• ..., però demà volem...

This is similar to English, where a comma before but is also very common when it joins two full clauses.

Because Catalan often uses the present tense for a future event that is already planned or intended.

So:

• demà volem fer l'excursió literally = tomorrow we want to do the excursion
• in natural English = tomorrow we want to go on the hike or tomorrow we’re planning to do the hike

This use of the present for future meaning is very common in Catalan, just as English can say Tomorrow we’re leaving.

Catalan uses fer very often for activities where English might use different verbs.

• fer una excursió = to go on an excursion / go on a hike / take a trip
• literally, to do the excursion

So volem fer l'excursió means they want to carry out that planned outing.

Because the feminine singular article la becomes l' before a vowel sound.

So:

• la muntanya
• l'excursió

This apostrophe is very common in Catalan and works much like it does in French or Italian: it avoids an awkward vowel clash.

The accent in excursió shows that the stress falls on the last syllable:

• ex-cur-si-ó

Without the accent, the stress pattern would be interpreted differently. In Catalan, written accents are very important because they often tell you both:

• where the stress goes
• sometimes what kind of vowel sound you have

So excursió must be written with the accent.