El meu germà ha trucat al timbre perquè no troba la clau.

In standard Catalan, a possessive usually comes with a definite article:

• el meu germà = my brother
• la meva mare = my mother

That is different from English, where we normally just say my brother without the.

You may sometimes see article-less forms in certain dialects or set expressions, but el meu germà is the normal standard pattern.

Ha trucat is the present perfect of trucar.

It is made with:

• ha = has
• trucat = called / rung

So literally it is something like has rung or has called.

In Catalan, this tense is often used for a past action that is still relevant now. In English, depending on context, you might translate it with either a present perfect or a simple past.

Yes, in many contexts va trucar would also be possible:

• El meu germà va trucar al timbre...

Va trucar is the common Catalan past tense often used for completed past events in narration.

Very roughly:

• ha trucat often feels more connected to the present situation
• va trucar often sounds more like a simple past event

The exact preference can vary by region and style, so both are worth learning.

Because al is the contraction of a + el:

• a el timbre → al timbre

This happens regularly in Catalan.

Also, trucar al timbre is the normal expression for to ring the bell / doorbell.

No. Trucar can also mean to call, especially on the phone.

For example:

• Trucar a la mare = to call Mum
• Trucar al timbre = to ring the doorbell

A useful thing to notice is that trucar normally takes a before the person or thing being called or rung.

Here perquè means because.

This is an important distinction:

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

So in your sentence:

• ...perquè no troba la clau = because he cannot find the key

The accent is part of the correct spelling of perquè in this meaning.

Because it describes a current situation: right now, he is not finding the key.

Catalan often uses the simple present where English might say:

• he can’t find the key
• he isn’t finding the key

So no troba la clau is very natural here.

If you said no ha trobat la clau, that would mean he hasn’t found the key, which focuses more on the result up to now.

In negative sentences, no trobar often works like English cannot find.

So:

• No troba la clau can mean He can’t find the key

Catalan does not always need a separate verb like can in cases like this. The simple verb is often enough to express the idea naturally.

Because Catalan often uses the definite article when the thing is already clear from context.

So la clau here means the key, and in context that is probably understood as his key or the key he needs.

If you wanted to be more explicit or contrast it with someone else’s key, you could say:

• la seva clau = his key / her key / their key

But in this sentence, la clau sounds perfectly natural.

Catalan often leaves out subject pronouns because the subject is already clear.

Here, the sentence already has:

• El meu germà

So adding ell would usually be unnecessary.

Catalan does this a lot:

• Ha trucat = He has rung / called
• No troba la clau = He can’t find the key

A subject pronoun like ell is mainly used for emphasis or contrast.

They mainly help show where the stress falls, and sometimes they also distinguish words.

• germà is stressed on the last syllable
• perquè is also stressed on the last syllable

For an English speaker, that is useful because stress matters in Catalan pronunciation. The accents help you avoid putting the stress in the wrong place.