bunkasai de gyouza wo tukuru ka douka, mada kimatte imasen.

かどうか means whether or not.

So:

• 餃子を作るかどうか = whether (we) will make gyoza or not

It turns the clause before it into an embedded yes/no question or uncertainty clause.

A useful pattern is:

• plain form + かどうか = whether ... or not

Examples:

• 行くかどうか分からない。 = I don’t know whether I’ll go.
• 買うかどうか考えている。 = I’m thinking about whether to buy it.

In your sentence, the thing that has not been decided is exactly this: whether to make gyoza at the cultural festival.

Because before かどうか, Japanese usually uses the plain form of the verb.

So:

• 作るかどうか = whether (someone) will make it
• not 作りますかどうか

This does not make the sentence casual overall. It is just the normal grammar for a clause placed before かどうか.

This is very common in Japanese:

• 行くかどうか
• 食べるかどうか
• できるかどうか

Even if the main sentence is polite, the verb before かどうか is usually plain.

Here, で marks the place/event where the action happens.

• 文化祭で餃子を作る = make gyoza at the cultural festival

You can think of で here as marking the setting of the action.

Compare:

• 学校で勉強する = study at school
• 公園で遊ぶ = play in the park
• 文化祭で餃子を作る = make gyoza at the school festival

A learner might wonder about に, but に is not natural here if you mean the place/event where the making happens. で is the normal choice for the location of an action.

Because 餃子 is the direct object of 作る.

• 餃子を作る = make gyoza

The particle を marks the thing directly affected by the action.

More examples:

• ご飯を食べる = eat a meal
• 本を読む = read a book
• ケーキを作る = make a cake

So in this sentence, 餃子 is the thing being made.

This is a very important difference.

• 決める = to decide something
• 決まる = to be decided

So:

• まだ決めていません = someone has not decided it yet
• まだ決まっていません = it has not been decided yet

Your sentence uses 決まっていません because the focus is on the state of the matter: the plan is still undecided.

This is often more natural in Japanese when talking about schedules, plans, rules, etc.

Compare:

• 誰が行くか、まだ決まっていません。 = It hasn’t been decided yet who will go.
• 誰が行くか、まだ決めていません。 = We haven’t decided yet who will go.

Both can be possible in some contexts, but they focus differently:

• 決まる = the result/state
• 決める = the act of deciding

まだ means still or not yet, depending on the sentence.

Here, with a negative verb:

• まだ決まっていません = has not been decided yet

So まだ shows that the decision is expected to happen later, but at this point it has not happened.

Compare:

• まだ食べていません。 = I haven’t eaten yet.
• まだ帰りません。 = I’m not going home yet.
• まだ決まっていません。 = It hasn’t been decided yet.

Without まだ, the sentence would simply say it is not decided, but まだ adds the nuance of up to now / so far.

Yes, something like we is probably implied in context, but Japanese often leaves subjects unstated when they are understood.

The sentence does not explicitly say:

• who would make the gyoza
• who is doing the deciding

That is very normal in Japanese.

From context, a listener would probably understand something like:

• our class
• our group
• the festival organizers
• we

So 餃子を作るかどうか naturally suggests whether we/our group will make gyoza.

And まだ決まっていません suggests it hasn’t been decided yet, without needing to state by whom.

Sometimes か alone can mean whether, but かどうか is often clearer and more explicit for a yes/no choice.

So:

• 餃子を作るかどうか = whether to make gyoza or not
• 餃子を作るか can also mean whether (we) will make gyoza, but it may sound less complete or less natural in some contexts

A rough way to think about it:

• かどうか strongly emphasizes whether or not
• か alone can sometimes work, especially in shorter or more direct phrasing

For learners, plain form + かどうか is a very safe and useful pattern.

The comma separates the long clause from the main statement.

Structure:

• 文化祭で餃子を作るかどうか = whether we will make gyoza at the cultural festival
• まだ決まっていません = has not been decided yet

So the comma helps the reader process the sentence more easily.

It is similar to writing:

• As for whether we’ll make gyoza at the festival, it hasn’t been decided yet.

In Japanese, commas are often used more flexibly than in English, so this comma is helpful but not always absolutely required.

It is polite overall because it ends with いません, part of the -ます style.

However, inside the sentence, 作る is in plain form because that is normal before かどうか.

So the sentence is a mix of:

• plain form inside the embedded clause
• polite form in the main predicate

This is completely normal Japanese.

You could make it more casual by saying:

• 文化祭で餃子を作るかどうか、まだ決まってない。

And more formal/written styles are also possible, but your original sentence is a very standard polite sentence.

No. In normal Japanese, this would usually be written without spaces:

文化祭で餃子を作るかどうか、まだ決まっていません。

Spaces are often added in learning materials to make the structure easier to see, but ordinary Japanese text does not usually separate words with spaces.

Yes. で here marks the event/location where the action takes place, so in natural English it could come out as:

• at the cultural festival
• during the cultural festival
• for the cultural festival

The exact English wording depends on context.

For example, if the group is planning a food stall, 文化祭で餃子を作る may really mean something like make/sell gyoza at the school festival. Japanese often leaves those practical details unstated if the situation is already understood.