När middagen är slut, diskar vi tillsammans.

Because Swedish uses verb-second word order in main clauses.

When a sentence starts with something other than the subject—here, the time clause När middagen är slut—the finite verb must come next in the main clause. So:

• När middagen är slut, diskar vi tillsammans.

Not:

• När middagen är slut, vi diskar tillsammans.

This is very common in Swedish:

• Idag jobbar jag hemma. = Today I’m working from home.
• Efter skolan går hon till gymmet. = After school, she goes to the gym.

So the pattern is:

• introductory element + verb
  • subject

Yes, here när means when.

In this sentence, När middagen är slut means When dinner is finished / When dinner is over.

Swedish när is used in many of the same ways as English when, especially for time clauses:

• När jag kommer hem, äter jag. = When I get home, I eat.
• Ring mig när du är klar. = Call me when you’re ready.

Because middagen means the dinner, while middag means dinner or a dinner depending on context.

Swedish often uses the definite form where English may or may not use the. Here:

• middag = dinner
• middagen = the dinner

In this sentence, it refers to the specific meal everyone is having, so middagen sounds natural.

Also notice that Swedish usually puts definiteness at the end of the noun:

• middag → middagen
• bok → boken = the book
• hus → huset = the house

Because slut is a very common Swedish word for finished, over, or at an end.

So:

• Middagen är slut = The dinner is over / Dinner is finished

This is a very natural Swedish way to express completion. Compare:

• Filmen är slut. = The movie is over.
• Kursen är slut. = The course is over.

English sometimes uses a verb (ends), but Swedish often prefers är slut in everyday speech.

Diskar is the present tense of diska, which means to do the dishes / wash the dishes.

So:

• diska = to do the dishes
• diskar = do/does the dishes, am/is/are doing the dishes depending on context

Examples:

• Jag diskar. = I’m doing the dishes / I do the dishes.
• Vi diskar tillsammans. = We do the dishes together / We’re doing the dishes together.

Swedish present tense does not change depending on the subject:

• jag diskar
• du diskar
• han/hon diskar
• vi diskar

Same form for all.

It usually corresponds to English do the dishes or wash the dishes.

The Swedish verb diska specifically refers to washing dishes, plates, cutlery, and similar kitchen items.

So diskar vi tillsammans can be understood as:

• we do the dishes together
• we wash up together

All are natural translations depending on the variety of English.

Because the verb diska already includes that meaning.

In English, you usually need an object:

• do the dishes
• wash the dishes

In Swedish, diska can stand on its own:

• Vi diskar. = We do the dishes.

So Swedish does not need to explicitly mention disken or tallrikarna here.

Tillsammans means together.

It often comes after the verb and subject in simple sentences:

• Vi diskar tillsammans. = We do the dishes together.
• De går hem tillsammans. = They go home together.

In your sentence:

• diskar vi tillsammans

the placement is completely natural.

The comma separates the introductory subordinate clause from the main clause:

• När middagen är slut, = subordinate time clause
• diskar vi tillsammans. = main clause

In Swedish, commas before the main clause after an introductory subordinate clause are common and often taught in standard written Swedish.

You may sometimes see variation in informal writing, but using the comma here is safe and standard.

Yes. It is a subordinate clause introduced by när.

A useful thing to notice is the word order inside it:

• När middagen är slut

Here the order is subject + verb:

• middagen = subject
• är = verb

That is normal for Swedish subordinate clauses.

Then the main clause follows:

• diskar vi tillsammans

And because the subordinate clause comes first, the main clause shows inversion: verb + subject.

So the whole sentence is a nice example of:

1. subordinate clause first
2. main clause with verb-second word order

Yes, you could, but it means something slightly different in tone.

• När middagen är slut = When dinner is finished/over
• När middagen har tagit slut = When dinner has come to an end / when dinner is finished up

är slut is simpler and very natural here.
har tagit slut is also common in Swedish, but it is often used for things that have run out or come to an end, for example:

• Mjölken har tagit slut. = The milk has run out.
• Filmen har tagit slut. = The movie has ended.

For your sentence, är slut is the most straightforward everyday choice.

Yes. Swedish present tense often covers both:

• a habitual action
• a present or near-future situation
• a general routine

So När middagen är slut, diskar vi tillsammans can mean:

• When dinner is over, we do the dishes together
  or
• After dinner, we usually do the dishes together

The exact meaning depends on context. Swedish present tense is often broader than English learners first expect.

Slut is pronounced approximately like sloot, but with a Swedish u sound that is not exactly the same as English oo.

A rough guide:

• sl as in English sl
• u = a rounded Swedish vowel, somewhat like saying ee while rounding your lips
• t at the end is clearly pronounced

If you are just starting, sloot is a decent approximation, but the vowel is more fronted and tighter in Swedish.

Also:

• är has a vowel somewhat like air, though not exactly
• middagen is roughly MID-da-yen in broad learner-friendly approximation
• tillsammans is roughly til-SAM-mans

Yes, absolutely.

This version is also correct:

• Vi diskar tillsammans när middagen är slut.

The difference is mainly emphasis and word order:

• När middagen är slut, diskar vi tillsammans.
  Focuses first on the time condition.
• Vi diskar tillsammans när middagen är slut.
  Starts with the main point: we do the dishes together.

Notice that if the main clause comes first, the normal order is:

• Vi diskar
  not
• Diskar vi

So the inversion only happens when another element comes first in the main clause.