Mobilen måste uppdateras igen, annars fungerar appen inte.

Because -en marks the definite form.

• mobil = a mobile phone
• mobilen = the mobile phone
• app = an app
• appen = the app

In Swedish, the equivalent of the is often attached to the end of the noun instead of being a separate word.

Yes. In everyday Swedish, mobil very commonly means mobile phone / cell phone. You do not need to say mobiltelefon every time.

So mobilen is a very natural way to say the phone when you mean a mobile phone.

Because måste is a modal verb. After modal verbs in Swedish, you normally use the bare infinitive, without att.

For example:

• Jag måste gå = I must go
• Du kan komma = You can come
• Mobilen måste uppdateras = The phone must be updated

This is similar to English, where you say must go, not must to go.

Uppdateras is the passive infinitive of uppdatera.

• uppdatera = to update
• uppdateras = to be updated

So:

• Mobilen måste uppdateras = The phone must be updated

The -s ending is a very common way to form the passive in Swedish.

It is passive, not reflexive.

In this sentence, -s does not mean the phone is doing something to itself. It means the action is being done to the phone.

So uppdateras here means be updated, not update itself.

Yes, that is also possible.

• Mobilen måste uppdateras igen
• Mobilen måste bli uppdaterad igen

Both mean roughly The phone must be updated again.

The first version, with the -s passive, is shorter and very natural, especially in instructions, system messages, and general statements. The bli + past participle version is also correct, but often feels a little heavier.

Because that is a natural position for igen in this kind of sentence.

• uppdateras igen = be updated again

Swedish often places adverbs like igen after the verb or verb phrase element they belong to. So this word order sounds normal and idiomatic.

Annars means otherwise or or else.

It connects the two parts of the sentence:

• Mobilen måste uppdateras igen = the necessary action
• annars fungerar appen inte = the result if that action is not done

So the logic is: The phone has to be updated again; otherwise, the app does not work.

Because Swedish main clauses follow the V2 rule: the finite verb usually comes in the second position.

Here, annars is placed first. That means the verb fungerar must come next:

• Annars fungerar appen inte

If the subject comes first, then you get:

• Appen fungerar inte

So when annars is moved to the front, the subject appen comes after the verb.

This is also part of normal Swedish word order.

Compare:

• Appen fungerar inte
• Annars fungerar appen inte

In the second clause, annars takes the first position, fungerar stays in second position, then comes the subject appen, and then inte.

So inte is not randomly at the end; it is following standard Swedish main-clause word order.