Bir sene sonra döneceğim.

• bir = one / a
• sene = year
• sonra = after / later
• döneceğim = I will return / I will come back

So the sentence is literally something like one year later I will return, and in natural English it is I’ll come back in a year or I’ll return after a year.

Yes. Sene and yıl both mean year.

• Bir sene sonra döneceğim
• Bir yıl sonra döneceğim

Both are natural and mean the same thing. Learners often hear sene a lot in everyday speech, while yıl can feel a bit more neutral or standard, but both are very common.

It can match either one, depending on context.

• If you are speaking from now, it usually means in a year.
• If you are telling a story about some past or future reference point, it can mean a year later.

So bir sene sonra is a general Turkish way to express that one-year time gap.

Because Turkish uses sonra after the word or phrase it relates to.

English says:

• after a year
• a year later

Turkish says:

• bir sene sonra

So this is normal Turkish structure. In this use, sonra behaves like a word that comes after the time expression.

That is a very common learner question, because sonra often appears with the ablative ending -den / -dan, as in:

• dersten sonra = after class
• yemekten sonra = after the meal

But with many expressions of amount of time, Turkish very often uses the bare form:

• iki gün sonra = in two days
• bir hafta sonra = in a week
• üç ay sonra = in three months
• bir sene sonra = in a year

So for this sentence, bir sene sonra is the normal, idiomatic choice.

It comes from the verb dönmek, which means to return, to come back, or to turn back.

It is built like this:

• dön- = verb stem
• -ecek = future tense suffix
• -im = I ending

So underneath, it is basically:

dön + ecek + im

In actual spelling and pronunciation, this becomes döneceğim.

Because of vowel harmony.

Turkish future tense has two forms:

• -ecek
• -acak

The verb stem dön- contains ö, which is a front vowel, so the future suffix appears as -ecek.

That is why you get:

• döneceğim = I will return

not

• dönacağım or dönacakım, which would be incorrect.

When the future suffix -ecek / -acak is followed by a vowel-initial personal ending, the final k often changes to ğ in spelling:

• gelecek + im → geleceğim
• yapacak + ım → yapacağım
• dönecek + im → döneceğim

So the ğ is the result of that sound/spelling change. It is not pronounced like a strong English g. It usually just softens the transition between vowels.

Because Turkish usually does not need a subject pronoun if the verb ending already shows the person.

In döneceğim, the ending already tells you the subject is I.

So:

• Bir sene sonra döneceğim = I’ll return in a year

If you want extra emphasis, you can add ben:

• Ben bir sene sonra döneceğim

That would mean something like I will return in a year, with more emphasis on the subject.

Turkish dönmek is broader than any single English verb. Depending on context, it can mean:

• return
• come back
• go back
• turn back

So in this sentence, döneceğim can naturally be translated as I’ll come back or I’ll return. Turkish does not always draw the exact same come/go distinction that English does here.

You may also hear:

• geri döneceğim

which adds the idea of back more explicitly.

Yes. Turkish word order is flexible.

The neutral, natural version is:

• Bir sene sonra döneceğim

But other orders are possible if you want to emphasize something:

• Döneceğim bir sene sonra

This is more marked and sounds like the speaker is especially focusing on in a year.

So the original sentence is the safest and most neutral order for learners.

A rough guide is:

dö-ne-je-yim

A few useful points:

• ö is not like English o. It is closer to German ö or French eu.
• Turkish c is pronounced like English j in jam.
• ğ is usually not a strong consonant sound. Here it mainly helps the vowels flow together.

So döneceğim sounds approximately like doh-neh-jeh-yeem, but with a true Turkish ö sound rather than plain English o.