Vi träffar läkaren den tolfte oktober.

Because träffar is the present tense form of the verb träffa.

• träffa = to meet / to see
• träffar = meet / are meeting / see / are seeing

So Vi träffar läkaren means We meet / are meeting / are seeing the doctor.

Also, Swedish often uses the present tense for planned future events, especially when a time is given. So this sentence can refer to a future appointment.

Because läkaren is the definite singular form, meaning the doctor.

The noun is:

• en läkare = a doctor
• läkaren = the doctor

So the ending shows definiteness. English uses a separate word, the, but Swedish often adds definiteness to the noun itself.

In Swedish, you usually do not use a preposition like on before a specific date in this kind of sentence.

So Swedish says:

• Vi träffar läkaren den tolfte oktober.

where English says:

• We’re seeing the doctor on October twelfth.

This is very normal in Swedish date expressions.

That is a standard Swedish way to say a date:

• den
  • ordinal number
    • month

So:

• den tolfte oktober = the twelfth of October / October twelfth

Here:

• den = the
• tolfte = twelfth
• oktober = October

In speech, this pattern is very common.

Because the ordinal form of tolv is irregular:

• tolv = twelve
• tolfte = twelfth

This is just something you need to learn as a set form. Swedish ordinals are not all perfectly predictable, so tolfte is the standard form.

In Swedish, months are not normally capitalized.

So you write:

• oktober
• januari
• maj

The same is true for days of the week:

• måndag
• tisdag

They only get a capital letter if they start a sentence.

Yes. träffa can mean both meet and see, depending on context.

For example:

• träffa en vän = meet/see a friend
• träffa läkaren = see the doctor

In English, see the doctor sounds more natural, but Swedish still uses träffa very naturally in this situation.

Yes, but the verb still has to stay in the second position in a main clause, which is a very important Swedish rule.

The sentence as given is:

• Vi träffar läkaren den tolfte oktober.

You could also say:

• Den tolfte oktober träffar vi läkaren.

That version puts the date first for emphasis, but träffar still stays in second position.

Because Swedish often uses the present tense for future meaning when the context is clear, especially with schedules, plans, and appointments.

So both the grammar and the date make the future meaning clear:

• Vi träffar läkaren den tolfte oktober.

This is completely natural Swedish for a planned future event.

Using ska is possible in some contexts, but it changes the feel a bit:

• Vi ska träffa läkaren den tolfte oktober.

That can sound more like we are going to see the doctor or we will see the doctor, with a little more emphasis on intention or plan.

In everyday writing, Swedes very often use numerals:

• den 12 oktober
• sometimes just 12 oktober

But when reading it aloud, people commonly say:

• den tolfte oktober

So the fully written-out version in your sentence is especially useful for learning how the date is spoken.