Reiseforsikringen er gyldig.

Because Norwegian usually writes compound nouns as one word.

So reiseforsikringen is built from:

• reise = travel
• forsikring = insurance
• -en = the definite ending

So the whole noun is literally travel-insurance-the.

A useful rule: in Norwegian compounds, the last part is the main noun. That means forsikring determines the basic meaning and grammar of the whole word.

-en is the definite article attached to the noun. In English, this is usually the.

Compare:

• en reiseforsikring = a travel insurance policy / a travel insurance
• reiseforsikringen = the travel insurance

So Norwegian often puts the at the end of the noun instead of using a separate word before it.

Because that is how Norwegian normally marks definiteness with nouns: by adding an ending.

In a simple sentence like this, reiseforsikringen already includes the idea of the.

English:

• the travel insurance

Norwegian:

• reiseforsikringen

This is one of the biggest structural differences from English.

Er is the present tense of å være, which means to be.

So:

• jeg er = I am
• du er = you are
• han/hun er = he/she is
• vi er = we are

Unlike English, Norwegian does not change the verb much depending on the subject. The same form er is used for all persons in the present tense.

Here gyldig means something like:

• valid
• in force
• currently applicable

With insurance, it means the insurance is active and can be used; it has not expired and is not invalid.

You will also see gyldig with things like:

• Billetten er gyldig. = The ticket is valid.
• Passet er gyldig. = The passport is valid.

Yes, adjectives in Norwegian can change form, but in this sentence gyldig is in a very normal basic form.

Here it is a predicative adjective, meaning it comes after er and describes the subject:

• Reiseforsikringen er gyldig.

Some other forms you may meet are:

• gyldige for plural or definite contexts
  
  • Dokumentene er gyldige. = The documents are valid.

In this sentence, gyldig is the correct form.

Yes, in this sentence it is very similar to English:

• Reiseforsikringen = subject
• er = verb
• gyldig = subject complement/adjective

So the pattern is:

Subject + verb + adjective

However, Norwegian has an important rule called V2 in main clauses: the verb usually stays in the second position.

For example:

• Nå er reiseforsikringen gyldig. = Now the travel insurance is valid.

So even when another word comes first, er still stays second.

Yes, but the meaning changes.

• Reiseforsikringen er gyldig. = the travel insurance is valid
  This usually refers to a specific insurance already known in the conversation.

• En reiseforsikring er gyldig. = a travel insurance is valid
  This sounds more like you are introducing one insurance policy, or speaking less specifically.

So the original sentence points to a particular travel insurance, not just any one.

Yes, this is standard Bokmål.

You may also see a form like:

• Reiseforsikringa er gyldig.

That version uses the feminine definite ending -a, which is common in Nynorsk and also possible in some Bokmål usage depending on style and noun gender choices.

So both forms can mean the same thing, but reiseforsikringen is a very normal Bokmål form.

A rough guide is:

• reiseforsikringen ≈ RYE-seh-for-SIK-ring-en
• er ≈ a short air / ehr
• gyldig ≈ GÜL-dig or GYL-dig

A few notes:

• rei- sounds like English rye
• the y in gyldig is a Norwegian vowel that English does not really have
  
  • try saying ee while rounding your lips

The exact pronunciation varies a bit by region, but that approximation will help you get close.