chinguga ajik an bon yeonghwaneun seupoilleoreul halkka bwa yaegi an haeyo.

Here, 친구가 is the subject of the descriptive clause 아직 안 본.

The phrase 친구가 아직 안 본 영화 literally means:

• movie(s)
• that my friend
• has not seen yet

In Korean, when a noun is being described by a clause, the subject inside that clause often takes 이/가. So:

• 친구가 아직 안 본 영화 = the movie that my friend hasn’t seen yet

If you used 친구는, it would sound more like you were setting up friend as the topic of the whole sentence, which is not what this sentence is mainly doing.

This is a noun-modifying clause.

Break it down:

• 아직 = still / yet
• 안 = not
• 본 = seen
• 영화 = movie

The verb 보다 means to see/watch.
Its noun-modifying past form is 본, so:

• 본 영화 = a movie that someone saw / a seen movie
• 안 본 영화 = a movie that someone didn’t see
• 아직 안 본 영화 = a movie that someone hasn’t seen yet

So Korean places the whole descriptive part before the noun:

• 친구가 아직 안 본 영화 = movies that my friend hasn’t seen yet

Because 본 describes a completed action: having seen.

Compare:

• 보는 영화 = a movie someone is watching / watches
• 본 영화 = a movie someone has seen

In this sentence, the idea is not movies my friend is watching now, but movies my friend has not seen yet, so the past descriptive form 본 is used.

With negation:

• 안 보는 영화 = a movie someone does not watch / doesn’t watch in general
• 안 본 영화 = a movie someone has not seen

That second meaning is what fits here.

는 marks 영화 as the topic: as for movies my friend hasn’t seen yet...

So the sentence has a topic-comment structure:

• 친구가 아직 안 본 영화는
• 스포일러를 할까 봐 얘기 안 해요.

This gives the feeling of:

• When it comes to movies my friend hasn’t seen yet, I don’t talk about them because I might spoil them.

The 는 can also imply a bit of contrast, like:

• for those movies, I avoid talking
• but for movies my friend has already seen, talking might be fine

스포일러 is a loanword from English spoiler, and in Korean 스포일러를 하다 means to spoil something or to give spoilers.

So:

• 스포일러를 하다 = to spoil / to reveal spoilers

This may sound a little unusual to English speakers because English usually says spoil the movie or give spoilers, but Korean often uses a noun + 하다 pattern.

Examples:

• 스포일러 하지 마세요. = Please don’t spoil it.
• 결말 스포일러했어. = I spoiled the ending.

In your sentence, 스포일러를 할까 봐 means because I’m worried I might spoil it.

-(으)ㄹ까 봐 expresses worry, concern, or precaution about something that might happen.

So:

• 스포일러를 할까 봐 = because I’m afraid I might spoil it
• more literally: in case I spoil it

This pattern is often used when someone avoids doing something because of a possible bad result.

Examples:

• 늦을까 봐 일찍 나왔어요. = I left early because I was worried I might be late.
• 비 올까 봐 우산을 가져왔어요. = I brought an umbrella in case it rains.

In your sentence:

• 스포일러를 할까 봐 얘기 안 해요 = I don’t talk about it because I might spoil it

It is not just simple cause-and-effect; it includes the speaker’s concern.

Yes, but the nuance changes.

• 안 본 영화 = movie(s) my friend hasn’t seen
• 못 본 영화 = movie(s) my friend couldn’t see / hasn’t been able to see

So:

• 안 본 is neutral and simply says the action did not happen
• 못 본 suggests inability, lack of opportunity, or some reason it wasn’t possible

In this sentence, 안 본 is the more natural general choice if you simply mean movies my friend hasn’t seen yet.

If you said:

• 친구가 아직 못 본 영화는...

it could sound like movies my friend hasn’t been able to watch yet, which is possible, but slightly different.

얘기하다 means to talk, to speak about, or to discuss.
말하다 means to speak/say.

Both can work in many situations, but 얘기하다 often feels very natural when talking about discussing a topic.

So:

• 영화 얘기 안 해요 = I don’t talk about the movie
• 그 얘기 안 해요 = I don’t talk about that

In this sentence, 얘기 안 해요 sounds very conversational and natural.

Also, 안 해요 is the casual polite spoken style of negation. A more formal or textbook-like version would be:

• 얘기하지 않아요

But in everyday Korean, 안 해요 is very common.

Yes, you can think of the object/topic of 얘기하다 as being understood from context.

The sentence literally says:

• As for movies my friend hasn’t seen yet, I don’t talk, because I might spoil them.

In natural English, we would usually say:

• I don’t talk about movies my friend hasn’t seen yet, because I might spoil them.

Korean often leaves out words that are obvious from context. After 영화는, it is already clear what the speaker means they do not talk about.

You could make it more explicit with something like:

• 그 영화 얘기는 안 해요.
• 줄거리는 얘기 안 해요.

But the original sentence is perfectly natural as it is.

It is the speaker.

The meaning is:

• I don’t talk about movies my friend hasn’t seen yet, because I’m worried I might spoil them.

Even though Korean often omits subjects, the final action 얘기 안 해요 clearly belongs to the speaker, so the worrying in 할까 봐 also naturally belongs to the speaker.

So the implied meaning is:

• 제가 스포일러를 할까 봐 얘기 안 해요. = I don’t talk about it because I might spoil it.

It does not mean the friend might spoil it.

A useful way to chunk it is:

• 친구가 아직 안 본 영화는
  = as for movies my friend hasn’t seen yet

• 스포일러를 할까 봐
  = because I’m worried I might spoil them

• 얘기 안 해요
  = I don’t talk about them

So the full flow is:

1. set up the topic: movies my friend hasn’t seen yet
2. give the reason: I might spoil them
3. give the action: so I don’t talk about them

This is a very common Korean sentence pattern: [topic] + [reason] + [main action]

Yes. Korean nouns often do not show singular/plural clearly unless needed.

So 영화는 could mean:

• the movie my friend hasn’t seen yet
• movies my friend hasn’t seen yet

In this sentence, English often translates it as movies because that sounds natural in a general statement:

• I don’t talk about movies my friend hasn’t seen yet...

But depending on context, it could also refer to one specific movie:

• As for the movie my friend hasn’t seen yet, I don’t talk about it because I might spoil it.

Korean leaves that number flexible unless the context makes it specific.

Yes, very natural.

It has several features of everyday spoken Korean:

• 안 해요 instead of 하지 않아요
• 얘기하다 as a casual, common verb for talk about
• 스포일러 as a very common modern loanword
• omission of words that are understood from context

A slightly more explicit version might be:

• 친구가 아직 안 본 영화는 제가 스포일러를 할까 봐 얘기 안 해요.

But the original sounds more natural because Korean usually leaves out obvious subjects like 제가.