Jeg bliver nervøs, hvis lynlåsen går i stykker igen.

Because bliver means becomes / gets, while er means is.

So:

• Jeg er nervøs = I am nervous
• Jeg bliver nervøs = I get nervous / I become nervous

In this sentence, the speaker is talking about a reaction that happens if the zipper breaks again, so bliver is the natural choice.

It can feel a bit like future in English, but Danish often uses the present tense for future or general situations.

So Jeg bliver nervøs, hvis ... means something like:

• I get nervous if ...
• I’ll get nervous if ...

The exact English translation depends on context, but the Danish present tense is completely normal here.

Use hvis for if and når for when.

• hvis = the event is possible, but not certain
• når = the event is expected or treated as something that will happen

So:

• Jeg bliver nervøs, hvis lynlåsen går i stykker igen = I get nervous if the zipper breaks again
• Jeg bliver nervøs, når lynlåsen går i stykker would sound more like I get nervous when the zipper breaks, suggesting that this is something that does happen

Here, hvis fits because the speaker is talking about a possibility.

Lynlåsen is the definite form: the zipper.

The base word is:

• en lynlås = a zipper

Definite singular:

• lynlåsen = the zipper

Danish usually adds the definite article to the end of the noun instead of putting a separate word in front, so:

• en bog = a book
• bogen = the book

The sentence is talking about a specific zipper, so lynlåsen is used.

Går i stykker is a very common Danish expression meaning breaks, comes apart, or stops working.

Literally, it is something like goes into pieces, but you should learn it as a fixed expression.

Examples:

• Min telefon gik i stykker = My phone broke
• Lynlåsen går i stykker = The zipper breaks

The verb gå has many idiomatic uses in Danish, so this is one of those cases where the literal meaning of go is not the important thing.

Yes, sometimes, but the nuance is a little different.

• går i stykker = breaks / stops functioning
• bliver ødelagt = gets damaged / gets ruined / is destroyed

For a zipper, går i stykker sounds very natural, because it suggests that it stops working properly.
Bliver ødelagt is possible, but it can sound a bit more general or more dramatic depending on context.

So lynlåsen går i stykker is probably the most idiomatic choice here.

Because after hvis, you have a subordinate clause, and Danish subordinate clauses do not use the normal main-clause verb-second pattern.

Main clause:

• Lynlåsen går i stykker igen
  Subject + verb + rest

Subordinate clause:

• hvis lynlåsen går i stykker igen
  hvis
  • subject + verb + rest

So after hvis, the subject lynlåsen comes before the verb går.

Igen means again, and in this sentence it naturally comes late in the clause:

• hvis lynlåsen går i stykker igen

That placement is very normal in Danish. It modifies the whole event: the zipper breaking again.

You can sometimes move adverbs around for emphasis, but the version in the sentence is the most neutral and natural one.

Because hvis lynlåsen går i stykker igen is a subordinate clause.

In Danish, many writers put a comma before subordinate clauses like this. You will often see:

• Jeg bliver nervøs, hvis lynlåsen går i stykker igen.

Depending on the comma system being used, the sentence may also appear without that comma, but the version with the comma is very common and completely normal.

A rough guide:

• nervøs: something like ner-VUHS
• lynlåsen: roughly lun-LOH-sen or lyn-LOH-sen, depending on how finely you want to imitate Danish sounds

A few pronunciation notes:

• The y in lynlås is not like normal English y. It is a front rounded vowel, which many English speakers find tricky.
• å sounds roughly like the vowel in law for many learners.
• Danish pronunciation is often softer and less clearly pronounced than spelling suggests.

If you want to sound natural, lynlåsen is worth practicing slowly in parts:

• lyn
• lås
• -en

Then combine them: lyn-lås-en.

Yes, nervøs is an adjective, and here it works like a subject complement after bliver.

In this sentence:

• Jeg = subject
• bliver = verb
• nervøs = adjective describing the subject

With jeg, the basic form nervøs is correct.

You may see other forms in other contexts, for example:

• et nervøst smil = a nervous smile
• nervøse mennesker = nervous people

So yes, it is an adjective, and yes, it can change form, but in this sentence the plain form nervøs is the right one.