Hon vill fira lugnt hemma i år, eftersom hon har varit lite förkyld hela veckan.

After the modal verb vill (want to), Swedish normally uses the bare infinitive of the next verb, without att.

• Hon vill fira = She wants to celebrate
• Jag vill gå = I want to go
• Vi vill stanna = We want to stay

This is like English, where we also do not say wants to to celebrate.

Here lugnt means something like quietly, calmly, or in a low-key way.

The base adjective is lugn = calm / quiet.
When Swedish uses an adjective adverbially, it often takes the -t form:

• en lugn kväll = a calm evening
• att fira lugnt = to celebrate quietly / in a calm way

So lugnt is functioning like an adverb here, describing how she wants to celebrate.

Hemma means at home, while hem usually means home in the sense of toward home.

So:

• Hon är hemma = She is at home
• Hon går hem = She goes home

In this sentence, she wants to celebrate at home, so hemma is correct.

I år means this year.

Literally, it is in year, but in Swedish this is the normal way to say this year:

• i dag = today
• i morgon = tomorrow
• i år = this year

So hemma i år means at home this year.

Eftersom means because / since and introduces a reason.

• Hon vill fira lugnt hemma i år, eftersom hon har varit lite förkyld hela veckan.
• She wants to celebrate quietly at home this year, because she has been a little under the weather all week.

It is similar to för att in many contexts, but eftersom often sounds a bit more clearly causal or explanatory in written Swedish.

Both can often translate as because, but learners should know:

• eftersom = because / since
• för att = because / in order to, depending on context

So för att can sometimes be ambiguous, while eftersom is clearly giving a reason here.

Har varit is the present perfect of vara (to be).

• är = is
• var = was
• har varit = has been

The sentence uses har varit because it describes a condition that started in the past and is relevant up to now:

• hon har varit lite förkyld hela veckan = she has been a little sick all week

This is very natural because hela veckan suggests a period continuing up to the present moment.

Förkyld means having a cold or suffering from a cold.

It does not mean cold in the sense of temperature. For that, Swedish uses kall.

Compare:

• Jag är kall. = I am cold.
• Jag är förkyld. = I have a cold.

So in this sentence, lite förkyld means a little under the weather / slightly sick with a cold.

Here lite means a little / somewhat / slightly and softens the adjective förkyld.

So:

• lite förkyld = a little sick / slightly under the weather / somewhat having a cold

It does not mean she is only a tiny bit physically cold. It means the illness is mild.

Swedish often uses lite this way to make something sound less strong:

• lite trött = a little tired
• lite sjuk = a little sick
• lite dyrt = a bit expensive

In Swedish, time expressions like hela veckan often appear without a preposition.

• hela veckan = all week
• hela dagen = all day
• hela året = all year

So:

• hon har varit lite förkyld hela veckan = she has been a little sick all week

This is very similar to English, which also says all week, not during all the week in normal usage.

It actually does affect the word order inside its clause.

In a main clause, Swedish usually has the verb in second position:

• Hon vill fira lugnt hemma i år

But after a subordinating conjunction like eftersom, Swedish uses subordinate clause word order, where the subject comes before the finite verb:

• eftersom hon har varit lite förkyld hela veckan

Notice that it is:

• hon har varit

not

• har hon varit

That is normal subordinate clause order in Swedish.

Yes, absolutely.

You could say:

• Eftersom hon har varit lite förkyld hela veckan vill hon fira lugnt hemma i år.

This means the same thing. The main difference is emphasis:

• Starting with Hon vill... puts focus first on what she wants
• Starting with Eftersom... puts focus first on the reason

Also notice that when a subordinate clause comes first, the main clause still follows Swedish V2 word order:

• Eftersom hon har varit lite förkyld hela veckan vill hon fira lugnt hemma i år.

Not:

• ... hon vill fira ...

Fira can be used both with and without an object.

With an object:

• fira jul = celebrate Christmas
• fira en födelsedag = celebrate a birthday

Without an object, it can simply mean celebrate in a general sense:

• Vi ska fira i kväll. = We’re going to celebrate tonight.

So Hon vill fira lugnt hemma i år is perfectly natural even without saying exactly what she wants to celebrate.

The comma is a punctuation choice separating the main clause from the explanatory subordinate clause.

• Hon vill fira lugnt hemma i år, eftersom hon har varit lite förkyld hela veckan.

In Swedish, commas before subordinate clauses are not always strictly required in every case, but they are often used when the writer wants clearer separation, especially in longer sentences.

So the comma here is natural and helps readability, but the grammar of the sentence does not depend on it.