Den svære sætning oversættes bedst i ro og mag.

Because sætning is a common-gender noun in Danish: en sætning.

In Danish, singular nouns are either:

• common gender → en
• neuter gender → et

So when the noun is definite, you use den with common-gender nouns and det with neuter nouns.

• en sætning = a sentence
• den ... sætning = the ... sentence

If the noun were neuter, you would use det instead.

This is a very common Danish feature called double definiteness.

When a noun is definite and has an adjective before it, Danish usually uses:

• a separate definite article: den / det / de
• the adjective in definite form
• the noun in its definite form

So:

• en svær sætning = a difficult sentence
• den svære sætning = the difficult sentence

Here, both den and sætning-en are expected. English learners often find this unusual, because English only uses one the.

Because the adjective is in the definite form.

Danish adjectives change form depending on what they describe. Compare:

• en svær sætning = a difficult sentence
• et svært ord = a difficult word
• den svære sætning = the difficult sentence

So:

• svær = common gender singular indefinite
• svært = neuter singular indefinite
• svære = definite form and also plural form in many cases

Since sætning is part of a definite phrase, svære is the correct form.

Oversættes is the present passive form of oversætte.

• oversætte = to translate
• oversætter = translates / is translating
• oversættes = is translated

So the sentence is not saying that the sentence itself actively translates something. It means the sentence is translated.

This -s passive is very common in Danish, especially in neutral statements, general truths, instructions, and formal style.

Yes. Den svære sætning bliver bedst oversat i ro og mag is possible.

Both forms can express the passive, but there is often a stylistic difference:

• oversættes = shorter, more neutral, often more general or formal
• bliver oversat = also passive, sometimes a bit more dynamic or conversational

In this sentence, oversættes sounds very natural because it describes the best way to do something in general.

Bedst means best and is the superlative form.

The forms are:

• god = good
• bedre = better
• bedst = best

Here it works adverbially, because it describes how the sentence is translated:

• oversættes bedst = is translated best

So bedst modifies the verb idea, not the noun.

It is a fixed idiomatic expression meaning something like:

• calmly
• without rushing
• at leisure
• in peace and quiet

Literally, it is something like in calm and ease, but that literal breakdown is less important than the fact that it functions as an idiom.

A useful point for learners: mag is not a very common everyday word on its own in modern Danish. Many learners first meet it in the expression i ro og mag.

Because i ro og mag is a fixed expression, not a literal noun phrase where you would normally expect articles.

Many idioms in Danish, just like in English, do not behave in a fully predictable word-for-word way. Compare English expressions like:

• at home
• in peace
• by car

So it is best to learn i ro og mag as one chunk.

The structure is:

• Den svære sætning = subject
• oversættes = finite verb, passive
• bedst = adverb/superlative
• i ro og mag = adverbial expression

So the pattern is essentially:

Subject + verb + adverb + adverbial phrase

This is normal Danish main-clause word order.

In this sentence, it most naturally means the difficult sentence.

Danish den can sometimes correspond to English that in other contexts, but here it is simply the ordinary definite article used in a definite noun phrase with an adjective.

So you should read:

• den svære sætning = the difficult sentence

not especially that difficult sentence, unless the wider context suggests contrast or pointing something out.