Hvis glidelåsen sitter fast, tar hun av beltet og bytter til en skjorte med korte ermer.

Because glidelåsen is the definite singular form of glidelås (zip / zipper).

• en glidelås = a zipper
• glidelåsen = the zipper

Norwegian usually adds the definite article as an ending instead of using a separate word like English the.

So here, glidelåsen means the zipper, probably a specific one already understood from context.

Sitter fast means is stuck or is jammed.

Literally, sitte means sit, but in Norwegian it is also used in expressions for how something is positioned or lodged. So sitter fast gives the idea that something is stuck in place.

Examples:

• Døra sitter fast. = The door is stuck.
• Lokket sitter fast. = The lid is stuck.

So this is a very natural Norwegian expression, even if it sounds a bit strange when translated word-for-word.

Because Norwegian main clauses follow the V2 rule: the finite verb must come in the second position.

The first part, Hvis glidelåsen sitter fast, is a subordinate clause. When that whole clause comes first, the main clause still has to put the verb first within its own structure:

• Hvis glidelåsen sitter fast, tar hun av beltet.

Not:

• Hvis glidelåsen sitter fast, hun tar av beltet.

So after an opening clause like hvis ..., Norwegian normally puts the main verb before the subject in the next clause:

• Hvis ..., tar hun ...

Because ta av is a phrasal verb meaning take off / remove.

In Norwegian, these little particles like av, på, opp, ut are often separated from the verb in main clauses.

So:

• Hun tar av beltet. = She takes off the belt.

But in an infinitive form, they stay together:

• å ta av beltet = to take off the belt

This is similar to English:

• She takes off the belt
• to take off the belt

Beltet is the definite singular form of et belte.

• et belte = a belt
• beltet = the belt

The sentence uses beltet because it refers to a specific belt, not just any belt.

This is very common in Norwegian when the object is understood from the situation.

Bytter til means changes to or switches to.

• å bytte = to change / exchange / switch
• å bytte til noe = to switch to something

So:

• bytter til en skjorte = changes to a shirt

It suggests moving from one thing to another.

Examples:

• Hun bytter til joggesko. = She changes into sneakers / switches to sneakers.
• Jeg bytter til norsk. = I switch to Norwegian.

This means a shirt with short sleeves.

Breakdown:

• en skjorte = a shirt
• med = with
• korte ermer = short sleeves

Why korte? Because ermer is plural (sleeves), and the adjective must agree with it:

• en kort erm = a short sleeve
• korte ermer = short sleeves

So:

• med korte ermer = with short sleeves

This is a very natural way to describe clothing in Norwegian.

Yes. En kortermet skjorte is also correct and natural.

Both mean essentially the same thing:

• en skjorte med korte ermer = a shirt with short sleeves
• en kortermet skjorte = a short-sleeved shirt

The first version is a little more descriptive and transparent for learners. The second is more compact.

Because ermer is plural, so the adjective must also take the plural form.

Adjective agreement:

• kort erm = short sleeve (singular, indefinite)
• korte ermer = short sleeves (plural)

So the -e ending on korte is there because ermer is plural.

Sometimes, yes, but not always.

In this sentence, hvis is the normal choice for a condition:

• Hvis glidelåsen sitter fast ... = If the zipper is stuck ...

Om can sometimes also mean if/whether, but it is often used more for whether than for a real condition.

Examples:

• Jeg vet ikke om hun kommer. = I don’t know whether she is coming.
• Hvis hun kommer, går vi. = If she comes, we leave.

So here, hvis is the clearest and most natural word.

Yes, sitter fast is more idiomatic for something physically stuck.

• Glidelåsen sitter fast. = The zipper is stuck / jammed.

Using er fast would usually sound less natural here. Fast with sitte is a common set expression for objects that are jammed, attached, or stuck in place.

So for a zipper, sitter fast is the phrase learners should remember.