Aktivitetsplanen endres etter arbeidstidsreduksjonen.

Because -en is the definite singular ending, roughly equivalent to English the.

• aktivitetsplan = activity plan
• aktivitetsplanen = the activity plan

In Norwegian, the definite article is often attached to the end of the noun instead of standing in front of it.

That -s- is a linking sound used in many Norwegian compound nouns.

• aktivitet
  • plan → aktivitetsplan
• arbeidstid
  • reduksjon → arbeidstidsreduksjon

It does not mean possession here. It is just part of how the compound is formed. English learners often notice it because it can look like an apostrophe-s idea, but it is not functioning that way.

Endres is the present tense s-passive form of endre.

• endre = to change
• endrer = changes / is changing
• endres = is changed / gets changed

So Aktivitetsplanen endres means that the activity plan is being changed, without saying who is doing the changing.

Because the sentence is focusing on what happens to the plan, not on who changes it.

Compare:

• Vi endrer aktivitetsplanen. = We change the activity plan.
• Aktivitetsplanen endres. = The activity plan is changed.

So endrer is active, while endres is passive.

Yes. That is also correct.

Both of these can mean roughly the same thing:

• Aktivitetsplanen endres
• Aktivitetsplanen blir endret

The difference is mostly style:

• endres often sounds more formal, compact, or administrative
• blir endret can sound a bit more explicit and is very common in everyday language

In official writing, the s-passive form is especially common.

Here etter most naturally means after or following.

So the idea is that the change to the activity plan happens after the reduction in working hours.

Depending on context, etter can sometimes feel slightly broader, like in response to or following, but the basic meaning is still temporal: one thing happens after another.

It is a compound noun made from smaller parts:

• arbeidstid = working time / work hours
• reduksjon = reduction
• arbeidstidsreduksjon = reduction in working hours
• arbeidstidsreduksjonen = the reduction in working hours

Again, the definite ending -en is attached to the whole compound at the end.

Because the sentence is referring to specific, identifiable things:

• the activity plan
• the reduction in working hours

This is very natural in Norwegian, especially in administrative or workplace contexts where both speaker and listener know which plan and which reduction are being discussed.

English and Norwegian do not always use definiteness in exactly the same way, but here the definite forms are completely normal.

This sentence has normal Norwegian main-clause word order:

• Aktivitetsplanen = subject
• endres = verb
• etter arbeidstidsreduksjonen = adverbial phrase

So it follows the common pattern subject + verb + other information.

You can also move the time phrase to the front:

• Etter arbeidstidsreduksjonen endres aktivitetsplanen.

Notice that the verb still stays in second position. That is a very important Norwegian rule in main clauses.

Yes, somewhat. It sounds like something you might read in a workplace notice, policy text, or official message.

The formal feel comes from things like:

• long compound nouns
• the passive form endres
• the overall compact style

A more conversational version might be something like:

• Vi endrer aktivitetsplanen etter arbeidstidsreduksjonen.
• Aktivitetsplanen blir endret etter arbeidstidsreduksjonen.

The original sentence is perfectly natural, but it leans toward formal written Norwegian.