Om appen inte fungerar, måste du starta om mobilen.

Because Swedish adds the definite article to the end of the noun.

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

So -en here means the.

Both app and mobil are common-gender nouns, so their singular definite form usually ends in -en.

Om means if and introduces a condition.

So Om appen inte fungerar is an if-clause:

• If the app doesn’t work

It sets up the situation before the main statement:

• you must restart the phone

Because this is a subordinate clause introduced by om.

In Swedish subordinate clauses, inte usually comes before the finite verb.

So:

• Om appen inte fungerar = correct

Compare that with a main clause:

• Appen fungerar inte = The app isn’t working

This is a very important word-order pattern in Swedish:

• main clause: verb before inte
• subordinate clause: inte before verb

Because Swedish main clauses follow the verb-second rule.

When the sentence begins with something other than the subject — here, the whole if-clause comes first — the finite verb of the main clause must come next.

So the structure is:

• Om appen inte fungerar, måste du starta om mobilen.

Literally, the order is:

• If the app doesn’t work, must you restart the phone

But in natural English, that becomes:

• If the app doesn’t work, you must restart the phone

If the main clause came first, then you would say:

• Du måste starta om mobilen om appen inte fungerar.

In normal written Swedish, yes, it is standard to put a comma after an introductory subordinate clause like this one.

So:

• Om appen inte fungerar, måste du starta om mobilen.

The comma helps separate the condition from the main clause.

In very informal writing, some people may omit commas more often, but in careful written Swedish, this comma is a good idea.

Swedish often uses the simple present where English might use either:

• doesn’t work
• isn’t working

So appen inte fungerar can match English the app doesn’t work or the app isn’t working, depending on context.

This is completely normal in Swedish. You do not need a special continuous form like English is working.

Because måste is a modal verb, and modal verbs in Swedish are followed directly by the infinitive.

So:

• måste starta = must restart
• not måste att starta

This is similar to English:

• must restart
• not must to restart

Other common Swedish modal verbs work the same way:

• kan läsa = can read
• vill gå = want to go
• ska komma = will / shall come

Yes. Starta om is a verb plus particle, and together they mean restart or reboot.

• starta = start
• starta om = restart

So in this sentence, you should understand starta om as a single unit of meaning.

This kind of verb is very common in Swedish:

• stänga av = turn off
• sätta på = turn on
• logga in = log in

Yes. In Swedish, mobil very commonly means mobile phone / cell phone.

So:

• mobilen = the mobile phone

You may also hear:

• mobiltelefonen = the mobile phone

But mobilen is shorter and extremely common in everyday language.

Yes, often you could.

• mobilen specifically means the mobile phone
• telefonen can mean the phone

In many modern contexts, telefonen will still be understood as a mobile phone, but mobilen is more specific.

So both can work, but mobilen makes it clearer that we are talking about a smartphone/mobile device.

Yes, absolutely.

That version is also correct:

• Du måste starta om mobilen om appen inte fungerar.

The difference is mainly emphasis and sentence flow:

• Om appen inte fungerar, måste du starta om mobilen.

  • starts with the condition
  • sounds a bit more like an instruction based on a situation

• Du måste starta om mobilen om appen inte fungerar.

  • starts with the main action
  • may feel slightly more direct

Both are natural Swedish.

Usually yes. Måste expresses necessity.

• du måste starta om mobilen = you must restart the phone

In technical instructions, this is very common and does not always sound overly harsh. It can simply mean this is necessary.

If you wanted something softer, Swedish might use other expressions, but in troubleshooting instructions måste is very normal.

Because app is a standard modern Swedish word borrowed from English, just like in many other languages.

It behaves like a normal Swedish noun:

• en app
• appen
• appar
• apparna

So even though it comes from English originally, it is fully integrated into Swedish grammar.