Det er lige meget, om vi sidder her eller i haven.

Because lige meget is a fixed Danish expression that means something like of equal importance or all the same. In natural English, that is usually translated as it doesn’t matter.

So:

• Det er lige meget = It doesn’t matter
• literally, it is closer to it is equally much / it is all the same

You will hear this expression very often in everyday Danish.

Here det is a dummy subject or formal subject. Danish, like English, often needs a subject in this kind of sentence even when no specific thing is being referred to.

Compare:

• Det er lige meget = It doesn’t matter
• English also uses a non-specific it

So det here does not mean a particular it. It is just required by the grammar of the sentence.

In this sentence, om means whether.

So:

• om vi sidder her eller i haven = whether we are sitting here or in the garden

This is a very common use of om in indirect questions and whether/if clauses.

Important: this is not the om that means about.

For example:

• Vi taler om vejret = We are talking about the weather
• Jeg ved ikke, om han kommer = I don’t know whether he is coming

In your sentence, it is the second type.

Because om vi sidder her eller i haven is a subordinate clause.

Danish comma rules allow a comma before a subordinate clause if you use start comma, and many people do write it that way:

• Det er lige meget, om vi sidder her eller i haven.

You may also see it without that comma in modern Danish:

• Det er lige meget om vi sidder her eller i haven.

Both can be acceptable depending on the comma style being used.

Because after om, you are in a subordinate clause, and Danish does not use normal main-clause V2 word order there.

So the basic order is:

• om + subject + verb
• om vi sidder

Compare with a main clause:

• Vi sidder her.

In this example, the word order looks the same, but the important point is that subordinate clauses do not follow main-clause inversion rules.

A useful contrast:

• Main clause: Nu sidder vi her.
• Subordinate clause: ... om vi nu sidder her.

In the subordinate clause, sentence adverbs and similar elements behave differently.

Danish often uses position verbs where English would often just use be.

Common position verbs are:

• sidde = sit
• stå = stand
• ligge = lie
• hænge = hang

So vi sidder her can mean literally we are sitting here, but depending on context it can also feel like we are here / we’re sitting here hanging out here.

Using er would be more neutral and less physical:

• vi er her = we are here
• vi sidder her = we are sitting here

So sidder adds the idea that the people are seated.

It can mean either, depending on context.

Danish present tense usually does not make a formal distinction between:

• we sit
• we are sitting

So:

• vi sidder her can mean we sit here or we are sitting here

In this sentence, the natural English translation will often be we sit here or we are sitting here, depending on the wider context.

Because haven is the definite singular form of have.

• en have = a garden
• haven = the garden

So:

• i en have = in a garden
• i haven = in the garden

The sentence uses haven because it refers to a specific garden, probably one that both speakers already know about.

Yes, that is completely natural.

Both parts express location, so Danish can coordinate them with eller:

• her = here
• i haven = in the garden

This is similar to English:

• here or in the garden

They do not have to be identical grammatical shapes as long as they match well in meaning.

Yes. That is also correct.

• Det er lige meget = It doesn’t matter
• Det er ligegyldigt = It’s irrelevant / It doesn’t matter

Both are common, but lige meget often sounds a bit more everyday and conversational. Ligegyldigt can sound slightly more formal or a bit stronger, depending on context.

So in normal speech, det er lige meget is extremely common.

Here eller is just the normal word for or.

It connects the two alternatives:

• her
• i haven

Together with om, the structure is:

• om ... eller ... = whether ... or ...

So the sentence means that the choice between those two places makes no difference.

Not very naturally.

A very literal version would be something like:

• It is equally much whether we sit here or in the garden.

That is not natural English. The idiomatic English translation is:

• It doesn’t matter whether we sit here or in the garden.

This is a good example of why fixed expressions like det er lige meget should usually be learned as a whole, not translated word by word.