Learn Hardcore Swedish: Pappa är svag efter febern, så han behöver vila. - Dad is weak after the fever, so he needs to rest.

In Swedish, kinship terms can be used without a possessive when it’s clear from context you mean your own family member. So Pappa naturally means “Dad.” If you need to be explicit or you’re talking outside a family context, you’d say min pappa (“my dad”).

Should pappa be capitalized like English “Dad”?

Only because it starts the sentence here. In Swedish, kinship words are normally lowercase even when used as a form of address: Jag älskar dig, pappa. English capitalizes “Dad” used as a name; Swedish usually doesn’t.

Why is it febern (definite) and not just feber?

The definite form febern (“the fever”) is used because we’re referring to a specific, contextually known fever episode. Swedish often uses the definite for unique or previously known events/periods: efter operationen, under semestern. Saying efter feber is unidiomatic. Alternatives: efter att ha haft feber (“after having had a fever”) or efter feberperioden (“after the fever period”).

Could I say Pappan är svag or Min pappa är svag instead?

Pappan är svag = “The dad is weak” (refers to some specific dad, not naturally “my dad” unless context makes that clear).
Min pappa är svag = “My dad is weak” (explicit).
Pappa är svag = natural when speaking about your own father in a family context.

Why is there a comma before så?

Because så connects two main clauses: Pappa är svag …, så han behöver vila. Swedish usually places a comma between independent clauses when linked by conjunctions like så (and especially men, utan). You may sometimes see it omitted in informal writing, but the comma is standard here.

Is så han behöver vila the same as using därför or så att?

… , så han behöver vila. = “…, so he needs to rest.” (result).
… . Därför behöver han vila. = “Therefore he needs to rest.” Note the V2 order after the sentence adverb: Därför behöver han.
… , så att han behöver vila is possible but less idiomatic here; så att typically marks a result clause (“such that”), e.g. Han är så svag att han behöver vila (“He’s so weak that he needs to rest”). Use that pattern if you want to emphasize degree.

Why is it han and not honom?

Han is the subject pronoun (“he”). Honom is the object form (“him”). After så, we start a new main clause where “he” is the subject: han behöver vila.

Why svag and not svagt or svaga?

Predicative adjectives (after “to be”) agree with the subject:

Common-gender singular: Pappa är svag.
Neuter singular: Huset är stort.
Plural: Barnen är svaga.

Here, pappa is common gender singular, so svag.

Do I need att before vila after behöver?

No. With behöva (“need to”), Swedish normally uses a bare infinitive: han behöver vila. Saying behöver att vila sounds odd in standard Swedish.

Should it be vila or vila sig?

Both exist. Vila (no reflexive) is very common and perfectly natural: han behöver vila. Vila sig also occurs and can feel a bit more colloquial or emphasize the resting of oneself: han behöver vila sig. No big meaning difference here.

Is vila a verb or a noun in this sentence?

It can be understood as the verb infinitive (“needs to rest”). But Swedish also has the noun vila (“rest”), and behöver vila can also be read as “needs rest.” The two readings coincide in meaning here, so speakers don’t need to disambiguate.

Why not say Pappa är svag av febern?

You can, but it changes nuance:

svag efter febern = weak after the fever (time relation; he’s recovering now).
svag av febern = weak because of the fever (the fever is the cause; often understood as during or due to it).
In your sentence, the time-based “after” makes most sense.

What’s the word order rule in han behöver vila?

Main clauses follow the V2 rule: the finite verb is in second position. Here the subject han is first, and the verb behöver is second. After så, you still have a main clause, so V2 applies: [han] [behöver] [vila].

Any pronunciation tips for tricky parts?

är: ä = [ɛ], short, like “e” in “bed.”
svag: long a = [ɑː]; final g is a hard [g].
så: å = long [oː].
behöver: stress on the second syllable: be-HÖ-ver; ö = [øː].
febern: rn often merges to a retroflex nasal [ɳ] in many accents.
vila: long i = [iː].