Den här boken finns inte i lager längre, så jag måste vänta en vecka till.

In Swedish, här usually needs a demonstrative word with it: den, det, or de.

So:

• den här boken = this book
• det här huset = this house
• de här böckerna = these books

You cannot normally say här boken in standard Swedish.

Also notice that boken is in the definite form, so Swedish often uses a double marking of definiteness with this kind of phrase:

• den här boken
  literally something like the this book, but it simply means this book

This is a very common Swedish pattern.

Because boken is the definite form of bok.

• en bok = a book
• boken = the book

After den här, Swedish normally uses the definite noun form:

• den här boken = this book

So even though English says just this book, Swedish uses both:

• den här
  • boken

That is standard grammar.

Finns is the present tense of finnas, which often means to exist, to be found, or to be available, depending on context.

In this sentence:

• Den här boken finns inte i lager längre

it does not mean that the book has stopped existing. It means the book is not available in stock anymore.

So finns is often used in Swedish where English might say:

• is available
• is in stock
• can be found

Because Swedish commonly uses finns i lager to express that something is available in stock.

• finns i lager = is in stock
• finns inte i lager = is not in stock

Using är i lager is not the usual expression here. A native speaker would normally say finns i lager.

This is one of those cases where Swedish and English organize the idea differently:

• English: The book is in stock
• Swedish: The book exists/is available in stock

I lager means in stock.

• lager = stock, inventory, or storage supply depending on context
• i lager = in stock

Examples:

• Varan finns i lager. = The item is in stock.
• Varan finns inte i lager. = The item is not in stock.

So in your sentence, finns inte i lager means the book is unavailable because the seller does not currently have it in stock.

Here längre means any longer or anymore.

So:

• finns inte i lager längre = is no longer in stock

This use of längre is very common in negative sentences.

Examples:

• Jag bor inte där längre. = I don’t live there anymore.
• Hon jobbar inte här längre. = She doesn’t work here anymore.

A useful pattern to remember is:

• inte ... längre = not ... anymore / no longer

In Swedish main clauses, inte usually comes after the finite verb.

Here the finite verb is finns:

• Den här boken finns inte i lager längre

Structure:

• subject: Den här boken
• verb: finns
• negation: inte
• rest of sentence: i lager längre

This is normal Swedish word order. English often places not differently, but in Swedish the rule verb + inte is very important in main clauses.

Here så means so in the sense of therefore or as a result.

The sentence has two parts:

• Den här boken finns inte i lager längre
• så jag måste vänta en vecka till

So the meaning is:

• This book is no longer in stock, so I have to wait another week.

Swedish så is very common for connecting cause and result in everyday language.

Because Swedish modal verbs usually take the infinitive without att.

Måste is a modal verb, like can, must, should in English.

So:

• jag måste vänta = I must wait / I have to wait

Not:

• jag måste att vänta

Other examples:

• Jag kan simma. = I can swim.
• Du bör gå. = You should go.
• Vi vill äta. = We want to eat.

So after måste, you use the bare infinitive: vänta.

Måste often corresponds to both must and have to in English.

In many everyday contexts, English prefers have to, while Swedish naturally uses måste:

• Jag måste vänta = I have to wait / I must wait

So even if must sounds a bit strong or formal in English, måste is completely normal in ordinary Swedish.

Because till here means more, extra, or additional.

So:

• en vecka = a week
• en vecka till = one more week / another week

This is a very common Swedish pattern:

• en kopp till = one more cup
• två dagar till = two more days
• lite till = a little more

So jag måste vänta en vecka till means I have to wait another week.

No, not in this sentence.

Swedish till can have several meanings depending on context, including to, for, or more/additional. Here it clearly means more/additional.

So:

• en vecka till = another week

If Swedish wanted to say until, it would usually use till in a different structure, for example:

• till imorgon = until tomorrow
• till nästa vecka = until next week

But in en vecka till, the meaning is one more week, not until a week.

Yes, that is normal.

After så meaning so, Swedish usually continues with normal main-clause word order:

• så jag måste vänta en vecka till

That means:

• jag = subject
• måste = finite verb
• vänta = infinitive

So the order is straightforward: subject + verb.

This is different from some other Swedish conjunctions, which can trigger different word order in subordinate clauses. But here så is introducing a new main clause, so the word order stays normal.

It sounds very natural. It is the kind of sentence you could hear in a shop, read on a website, or say in conversation.

A few especially natural pieces are:

• den här boken = very common way to say this book
• finns inte i lager = standard expression for is not in stock
• längre = natural for anymore
• en vecka till = natural for another week

So this sentence is good idiomatic Swedish, not a word-for-word translation from English.