raigetu no ensoku ha, kouyou ga kireina yama ni iku yotei desu.

の links nouns together.

• 来月 = next month
• 遠足 = excursion / field trip

So 来月の遠足 means next month’s excursion or the excursion next month.

In this sentence, の works a lot like ’s or of in English.

は marks 遠足 as the topic of the sentence.

So the sentence is talking about as for next month’s excursion...

This does not necessarily mean 遠足 is the grammatical subject in the same way as English. It just means that this is the main thing the speaker is discussing.

A natural breakdown is:

• 来月の遠足は = as for next month’s excursion,
• 紅葉がきれいな山に行く予定です = it is planned to go to a mountain with beautiful autumn leaves

Here, が marks 紅葉 as the thing that is beautiful.

So:

• 紅葉がきれい = the autumn leaves are beautiful

This whole part then describes 山.

So 紅葉がきれいな山 literally means:

• a mountain [where] the autumn leaves are beautiful

or more naturally:

• a mountain with beautiful autumn leaves

This is a very common pattern in Japanese: a small clause comes before a noun and describes it.

Because きれい is a na-adjective.

When a na-adjective directly modifies a noun, you add な:

• きれいな山 = a beautiful mountain

Compare:

• 山はきれいです = the mountain is beautiful
• きれいな山 = a beautiful mountain

So the な only appears when the adjective comes directly before the noun.

Japanese often puts a full descriptive phrase before the noun it modifies.

So instead of saying:

• a mountain where the autumn leaves are beautiful

Japanese says:

• 紅葉がきれいな 山
• literally: [autumn leaves are beautiful] mountain

There is no word like where, that, or which required here. The whole phrase before 山 simply modifies 山.

This kind of structure is very important in Japanese.

Because 行く takes に to mark the destination.

• 山に行く = go to the mountain

So in this sentence:

• 紅葉がきれいな山に行く = go to a mountain with beautiful autumn leaves

You can think of に here as meaning to.

Because when a verb comes before 予定, it normally uses the dictionary form:

• 行く予定です = plan to go / be scheduled to go

Not:

• 行きます予定です ✘

This is a common pattern:

• V dictionary form + 予定です = plan to do V

Examples:

• 明日帰る予定です = I plan to go home tomorrow
• 来週会う予定です = I plan to meet next week

The sentence is still polite because it ends with です.

予定です means something like:

• is planned
• is scheduled
• the plan is to...

It sounds a little more formal or structured than simply saying 行きます.

Compare:

• 山に行きます = We will go to the mountain
• 山に行く予定です = We are planning to go to the mountain / It is scheduled that we will go

So 予定です suggests a plan or schedule, not just a simple future statement.

Japanese often leaves out subjects when they are understood from context.

In this sentence, the people going are probably the people involved in the excursion, such as:

• the class
• the students
• the group
• we

English usually needs a subject, but Japanese often does not.

So even though we is not written, the meaning is understood from context.

The comma is mainly there to show a pause and make the sentence easier to read.

• 来月の遠足は、紅葉がきれいな山に行く予定です。

It separates the topic from the rest of the sentence.

This kind of comma is common in Japanese writing, but it is not always strictly required. The sentence could still be understood without it.

Very natural in Japanese.

In English, you might translate it in several ways depending on style:

• a mountain where the autumn leaves are beautiful
• a mountain with beautiful autumn foliage
• a mountain known for its beautiful fall colors

Japanese often keeps things compact and descriptive in a way that may sound slightly more literal if translated word-for-word.

So the Japanese phrase is normal; it is just structured differently from English.

In this sentence, it is most likely read こうよう.

• 紅葉（こうよう） = autumn leaves / fall colors

You may also know 紅葉 as もみじ, but that reading is often associated more specifically with maple leaves or the word as a standalone seasonal term.

In a sentence like 紅葉がきれいな山, こうよう is the most likely reading.