Cal que comprem el regal avui, perquè demà és l'aniversari de la meva amiga.

Cal que is a very common Catalan way to say it is necessary that... or we need to....
The verb cal is used impersonally here, so it does not change to match we.

In this sentence, Cal que comprem el regal avui means something like It’s necessary that we buy the gift today.

After cal que, Catalan normally uses the subjunctive.

So in this sentence, comprem is the subjunctive form. For the nosaltres form of regular -ar verbs like comprar, the present subjunctive happens to look the same as the present indicative:

• indicative: comprem
• subjunctive: comprem

So even though the form looks identical, the grammar after cal que is subjunctive.

Yes.

• Cal que comprem el regal avui = it is necessary that we buy the gift today
• Cal comprar el regal avui = it is necessary to buy the gift today
• Hem de comprar el regal avui = we have to buy the gift today

All three are natural, but they are slightly different in tone. Cal sounds a bit more impersonal or objective, while hem de sounds more direct and personal.

El regal uses the definite article, so it refers to a specific gift, probably one both speakers already have in mind, such as the birthday present.

If you said un regal, it would sound more like a gift, any gift in general.

In standard Catalan, possessives usually go together with a definite article:

• el meu llibre
• la meva amiga
• els meus pares

So la meva amiga is the normal standard pattern. Omitting the article is generally not standard in this kind of everyday sentence.

Catalan possessives agree with the noun they describe in gender and number.

Here, amiga is feminine singular, so the possessive must also be feminine singular:

• el meu amic = my male friend
• la meva amiga = my female friend

It agrees with amiga, not with the speaker.

Here de marks possession or association. It works like English of or 's.

So l'aniversari de la meva amiga literally means the birthday of my friend, which in natural English would usually be my friend's birthday.

Catalan often uses this noun + de + possessor structure.

Because aniversari begins with a vowel, the masculine singular article el is shortened to l'.

So:

• el llibre
• l'aniversari

This is called elision. It is a normal spelling rule in Catalan.

That is a good question, because l' hides the gender.

You know it is masculine from the full article in other contexts or from the dictionary form:

• singular: l'aniversari
• plural: els aniversaris

The plural els shows clearly that it is masculine.

They are different words:

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

In this sentence, perquè introduces the reason: because tomorrow is my friend's birthday.

Catalan learners often confuse these, so it is worth noticing that perquè is written as one word here.

Because avui and demà are time adverbs, and Catalan uses them without a preposition, just like English uses today and tomorrow without on.

So:

• avui = today
• demà = tomorrow

Not en avui or a demà.

No, Catalan word order is fairly flexible, although this version is very natural and neutral.

You could also hear:

• Avui cal que comprem el regal
• Cal que avui comprem el regal

These alternatives shift the emphasis a little, but the basic meaning stays the same.

Accent marks in Catalan are important. They can show stress, and sometimes they also help distinguish between different words.

In this sentence:

• és has an accent to distinguish it from es
• perquè has an accent to show the stressed syllable
• demà has an accent because the stress falls on the last syllable

So the accents are not optional spelling marks; they are part of the correct written form.