I oktober blir kvällarna mörkare, men jag tycker om att läsa då.

Swedish normally uses i for months, seasons, and years when talking about time:

• i oktober = in October
• i november = in November
• i sommar = in summer
• i år = this year

So i oktober is the natural choice here. På is used in other time expressions, but not usually with months.

In Swedish, names of months are usually written with a lowercase letter, unlike in English.

So Swedish writes:

• oktober
• måndag
• svenska

not Oktober, Måndag, or Svenska, unless the word starts a sentence.

This is because Swedish follows the V2 rule in main clauses: the finite verb usually comes in the second position.

The sentence starts with I oktober, which takes the first position. That means the verb must come next:

• I oktober blir kvällarna mörkare

Not:

• I oktober kvällarna blir mörkare

A more basic word order would be:

• Kvällarna blir mörkare i oktober

Both are possible, but when you move I oktober to the front, the verb must stay second.

Here, blir means become or get.

So:

• kvällarna blir mörkare = the evenings become darker / the evenings get darker

It comes from the verb bli, which often means become, get, or sometimes be depending on context.

Kvällarna is the definite plural of kväll:

• en kväll = an evening
• kvällen = the evening
• kvällar = evenings
• kvällarna = the evenings

In Swedish, the definite plural is often used when speaking about a general set that is understood from context, especially in seasonal or habitual statements.

So kvällarna blir mörkare means something like the evenings get darker, referring to the evenings during that time of year.

Mörkare is the comparative form of mörk:

• mörk = dark
• mörkare = darker
• mörkast = darkest

Many Swedish adjectives form the comparative by adding -are and the superlative by adding -ast.

So:

• kvällarna blir mörkare = the evenings get darker

After tycker om when it is followed by another verb, Swedish normally uses att + infinitive:

• tycker om att läsa = like to read
• tycker om att simma = like to swim

So att läsa is the infinitive phrase to read.

This is similar to English like to read, though English can also say like reading. Swedish usually uses att in this pattern.

Tycker om means like or be fond of.

• Jag tycker om att läsa = I like reading / I like to read

It is very similar to gillar:

• Jag gillar att läsa

Both are natural. Very roughly:

• gillar can sound a bit more direct and everyday
• tycker om can sound slightly softer or more personal

In many situations, they are interchangeable.

Here, då means then, at that time, or when that happens.

So:

• men jag tycker om att läsa då = but I like to read then / at that time

It refers back to when the evenings get darker in October.

This då is not the same as every possible meaning of då in Swedish. In other contexts, it can also mean things like when or appear in fixed expressions, but here it clearly means then/at that time.

Putting då at the end is a very natural way to add then / at that time after the main idea.

• Jag tycker om att läsa då

This sounds smooth and conversational. Swedish often places short time words like this later in the clause when they refer back to something already mentioned.

You could also rearrange things, but this version is very idiomatic in context.

Because men means but and joins two main clauses:

• I oktober blir kvällarna mörkare
• men jag tycker om att läsa då

In Swedish, it is common to use a comma before men when it connects two complete clauses. This is similar to English punctuation in many cases.

Yes, absolutely. That version is also correct:

• Kvällarna blir mörkare i oktober, men jag tycker om att läsa då.

The difference is mainly focus:

• I oktober blir kvällarna mörkare... puts emphasis on October
• Kvällarna blir mörkare i oktober... starts more neutrally with the evenings

Both are grammatical and natural.