Efteråret er den årstid, som min kone bedst kan lide, men jeg foretrækker foråret.

In Danish, -et is often the definite article for a common-gender or neuter noun, attached to the end of the noun rather than written as a separate word.

Here:

• efterår = autumn, fall
• efteråret = the autumn / autumn
• forår = spring
• foråret = the spring / spring

With names of seasons, Danish often uses the definite form where English would usually just say autumn or spring.

So:

• Jeg foretrækker foråret = I prefer spring

Even though English has no the, Danish naturally uses the definite form here.

Danish often uses a double definite structure when there is a modifier before the noun.

Compare:

• årstiden = the season
• den årstid = that/the season
• den årstid, som ... = the season that/which ...

In the sentence, årstid is being specified by the relative clause som min kone bedst kan lide, so Danish uses den årstid.

This is very common:

• den bog, jeg læser = the book I am reading
• det hus, vi købte = the house we bought

So den årstid means the season in a structure that is being further described.

Som here is a relative pronoun, meaning that, which, or sometimes who, depending on context.

In this sentence:

• den årstid, som min kone bedst kan lide
  = the season that my wife likes best

So som connects den årstid to the clause describing it.

Danish often uses som where English uses that or which:

• manden, som bor der = the man who lives there
• bogen, som jeg købte = the book that I bought

In Danish, to like is very often expressed as kan lide, literally can like, but as a whole it simply means like.

So:

• jeg kan lide kaffe = I like coffee
• min kone kan lide efteråret = my wife likes autumn

In your sentence:

• bedst kan lide = likes best

This is a very common Danish expression, and learners should treat kan lide as a fixed phrase.

Bedst is the superlative adverb of godt and means best.

In Danish, adverbs like this typically come before the verbal expression they modify:

• jeg kan bedst lide te = I like tea best
• hun kan bedst lide sommeren = she likes summer best

So:

• som min kone bedst kan lide
  literally: that my wife best can like natural English: that my wife likes best

The Danish word order is normal here.

They are related, but not identical.

• kan lide = like
• foretrækker = prefer

So:

• min kone bedst kan lide = my wife likes best
• jeg foretrækker foråret = I prefer spring

You could think of the sentence as contrasting two ways of expressing preference:

• My wife’s favorite season is autumn.
• But I prefer spring.

Foretrække is a single verb meaning to prefer, and foretrækker is the present tense form.

Because this is a subordinate clause, introduced by som.

In Danish:

• main clauses usually have V2 word order: the finite verb comes in second position.
• subordinate clauses do not follow V2 in the same way.

So in a subordinate clause, the usual order is: subject + adverb + finite verb + infinitive/rest

That is exactly what we see here:

• som
  • min kone
    • bedst
      • kan lide

Compare:

• Main clause: Min kone kan bedst lide efteråret.
• Subordinate clause: ... som min kone bedst kan lide.

This difference is very important in Danish grammar.

Danish comma usage often places commas before:

• relative clauses, such as those introduced by som
• coordinating conjunctions like men, depending on the comma style being used

So here:

• den årstid, som min kone bedst kan lide
• ..., men jeg foretrækker foråret

The comma before som marks the relative clause. The comma before men separates the two main clauses:

• Efteråret er den årstid ...
• jeg foretrækker foråret

Learners should be aware that Danish comma rules are not always identical to English ones.

Usually, yes, in modern standard Danish.

• min kone = my wife

Historically or in some contexts, kone could also mean woman, but in everyday modern Danish, min kone clearly means my wife.

If you want to say woman in general, Danish more often uses:

• kvinde = woman

So in this sentence, min kone definitely means my wife.

Because Danish usually adds the definite article to the end of the noun instead of putting it in front.

English:

• the autumn
• the spring

Danish:

• efteråret
• foråret

This is one of the biggest differences from English. Danish has:

• an indefinite article before the noun: et forår = a spring
• a definite ending on the noun: foråret = the spring / spring

So the idea of the is present, but it is built into the noun itself.

Yes, it is completely natural.

The structure:

• X er den Y, som ... means:
• X is the Y that ...

So:

• Efteråret er den årstid, som min kone bedst kan lide = Autumn is the season that my wife likes best

This is a very normal and useful Danish pattern:

• Det er den bog, som jeg bedst kan lide = That is the book I like best
• Hun er den lærer, som børnene bedst kan lide = She is the teacher the children like best

Yes, that would also be possible, but it is a different structure.

• Efteråret er min kones yndlingsårstid
  = Autumn is my wife’s favorite season

That version is shorter and perhaps a bit more direct.

Your original sentence:

• Efteråret er den årstid, som min kone bedst kan lide literally describes autumn as the season that my wife likes best.

Both are natural, but the original is especially useful for learners because it shows:

• relative clauses with som
• the expression kan lide
• superlative bedst

The whole sentence is in the present tense.

• er = is
• kan lide = like / likes
• foretrækker = prefer / prefers

Danish present tense is usually quite simple in form. For many verbs, the present ends in -r:

• foretrække → foretrækker
• lide is part of the expression kan lide
• være → er

Even though English sometimes uses do/does or changes the verb more, Danish present-tense forms are often more straightforward.