Du kender jo min mor; hun bliver rolig, så snart alle er kommet sikkert hjem.

Jo is a very common Danish particle that adds a shared-knowledge feeling. Here it suggests something like you know / after all / as you know.

So Du kender jo min mor is not just You know my mother in a neutral way. It sounds more like the speaker is reminding the listener of something they both already know about her.

If you remove jo, the sentence is still grammatical, but it loses that extra tone of you know what she’s like.

Danish separates two ideas that English often covers with know:

• kende = know, be familiar with a person/place/thing
• vide = know a fact, piece of information, or proposition

So:

• Du kender min mor = You know my mother
• Du ved, at min mor bliver urolig = You know that my mother gets worried

Because the object here is a person, min mor, Danish uses kende.

The semicolon separates two full main clauses:

• Du kender jo min mor
• hun bliver rolig, så snart alle er kommet sikkert hjem

A semicolon shows that the two clauses are closely connected in meaning. A full stop would also work, but it would make the connection feel slightly less tight.

A plain comma between two full independent clauses is usually not the standard choice here.

Because så snart introduces a subordinate clause: så snart alle er kommet sikkert hjem.

In Danish comma rules, many writers place a comma before a subordinate clause. You may also see sentences without this comma, depending on the comma system being used. So this punctuation is normal and correct.

The important grammar point is that så snart starts a dependent clause.

Bliver rolig means becomes calm / gets calm, so it describes a change of state.

• er rolig = is calm
• bliver rolig = becomes calm

Here the idea is that she is not calm before everyone gets home, and then she calms down once they have arrived safely. That is why bliver fits better than er.

Because the adjective agrees with the subject.

Here the subject is hun, which is singular and not neuter, so the basic form rolig is used.

Compare:

• hun er/bliver rolig
• barnet er/bliver roligt
• de er/bliver rolige

So the form changes depending on who or what is being described.

Så snart means as soon as. It introduces the time clause that tells you when the action in the main clause happens.

So the structure is:

• main clause: hun bliver rolig
• time clause: så snart alle er kommet sikkert hjem

It emphasizes immediacy: the moment everyone has gotten home safely, she becomes calm.

Yes, but the nuance changes.

• så snart = as soon as, with a strong sense of immediacy
• når = when, more general and less precise about how quickly

So:

• hun bliver rolig, så snart alle er kommet sikkert hjem
  = she relaxes the moment everyone is safely home

• hun bliver rolig, når alle er kommet sikkert hjem
  = she becomes calm when everyone has gotten home safely

Both are possible, but så snart is more vivid and specific.

Because så snart introduces a subordinate clause, and subordinate clauses do not use normal main-clause verb-second order.

In a main clause, Danish often has V2 word order:

• Så bliver hun rolig

But in a subordinate clause, the subject normally comes before the finite verb:

• så snart alle er kommet sikkert hjem

So alle er is the expected subordinate-clause order.

The verb komme normally forms the perfect with være:

• han er kommet
• de er kommet hjem

So alle er kommet sikkert hjem is the normal perfect form.

This is one of those verb patterns that learners mostly need to memorize. With komme, Danish uses være in the perfect, not have.

Here sikkert means safely.

Danish sikkert can mean either:

• safely
• probably / surely

In this sentence, because it appears with kommet ... hjem, the meaning is get home safely:

• komme sikkert hjem = get home safely

If it meant probably, it would usually have a different position and a different feel, for example in a sentence like De er sikkert kommet hjem = They have probably gotten home.

Because hjem here is an adverb meaning home, not a noun meaning a home.

So Danish says:

• jeg går hjem = I’m going home
• de er kommet hjem = they have come home

But as a noun, it would be different:

• et hjem = a home

So in this sentence, hjem works like English home in get home, not like a regular noun.