Si plou diumenge, vull dormir més i descansar a casa.

Yes. Si means if in Catalan.

So:

• Si plou diumenge = If it rains on Sunday

A useful warning for English speakers: Catalan si can also mean yes in some contexts, but in this sentence it clearly means if.

In Catalan, weather verbs usually do not need a subject pronoun.

• Plou = It is raining / It rains
• Neva = It is snowing / It snows

English needs a dummy subject like it, but Catalan does not. So plou by itself is a complete sentence.

Plou is the 3rd person singular present of the verb ploure (to rain).

• ploure = to rain
• plou = it rains / it’s raining

In this sentence, Catalan uses the present tense in the if-clause, just like English often does:

• Si plou diumenge... = If it rains on Sunday...

Catalan often uses the day name without a preposition when talking about a specific day.

• diumenge = Sunday
• Si plou diumenge = If it rains on Sunday

English usually needs on, but Catalan often does not.

You may also see:

• el diumenge in some contexts, especially for habitual meaning or with some regional variation

But in this sentence, plain diumenge is completely natural.

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

• vull = I want
• so (jo) vull both mean I want

Because vull clearly marks the first person singular, jo is unnecessary unless you want emphasis or contrast.

For example:

• Jo vull dormir més, però ell no. = I want to sleep more, but he doesn’t.

This is a very common structure:

• vull = I want
• dormir = to sleep
• descansar = to rest

So:

• vull dormir més i descansar = I want to sleep more and rest

After vull (I want), Catalan uses the infinitive:

• vull dormir = I want to sleep
• vull descansar = I want to rest

This works much like English want + to + verb, except Catalan does not use a separate word for to here.

Because one vull can govern both infinitives:

• vull dormir més i descansar
  = I want to sleep more and rest

Catalan does not need to repeat vull unless you want extra emphasis or a different rhythm.

You could say:

• vull dormir més i vull descansar but that sounds more emphatic or repetitive.

Més means more.

So:

• dormir més = to sleep more

Depending on context, English might translate this as:

• sleep more
• sleep longer

Also note the accent:

• més = more
• mes = month

So the accent matters.

A casa means at home or to home/home depending on context.

In this sentence:

• descansar a casa = to rest at home

Catalan normally uses the preposition a here.

Compare:

• Sóc a casa. = I am at home.
• Em quedo a casa. = I’m staying home.
• Descanso a casa. = I rest at home.

No. In Catalan, as in English, a real future condition often uses the present tense after if.

• Si plou diumenge, vull dormir més...

This is natural Catalan. English also normally says:

• If it rains on Sunday... not
• If it will rain on Sunday...

So the tense choice here is normal and idiomatic.

Yes. Catalan word order is fairly flexible.

These are both possible:

• Si plou diumenge, vull dormir més i descansar a casa.
• Si diumenge plou, vull dormir més i descansar a casa.

The first one may feel slightly more neutral here, but both are understandable and natural. Changing the order can shift emphasis a little.

The comma separates the conditional clause from the main clause:

• Si plou diumenge, = if it rains on Sunday
• vull dormir més i descansar a casa. = I want to sleep more and rest at home

This is very common and helps readability. In short sentences, punctuation can vary a bit, but the comma is perfectly normal here.

Not with the same meaning.

• descansar a casa = to rest at home
• estar a casa = to be at home

So descansar tells you what you want to do, while estar only tells you where you are.

If your meaning is specifically about relaxing or taking it easy, descansar a casa is the better choice.

It sounds like a personal intention or preference for a possible situation.

• Si plou diumenge = if that situation happens
• vull dormir més i descansar a casa = that is what I want to do

So it is not a general truth like If it rains, streets get wet. It is more like a plan or desire connected to a possible future event.