sakura ga tiru mae ni, tomodati to hanami wo sitai desu.

Both are possible in some contexts, but が is very natural here because 桜 is the subject of the verb 散る.

• 桜が散る = the cherry blossoms fall
• 桜は散る would sound more like as for the cherry blossoms, they fall or could add contrast/emphasis

In this sentence, the speaker is simply setting up a time condition: before the cherry blossoms fall. For that kind of subordinate clause, が is very common.

Because 前に usually comes after the plain form of a verb when you mean before doing X or before X happens.

So:

• 桜が散る前に = before the cherry blossoms fall
• 桜が散った前に is not correct here

Even though the event is in the future from the speaker’s point of view, Japanese normally uses the plain non-past form before 前に.

前に means before.

In this sentence, it attaches to the whole clause:

• 桜が散る前に = before the cherry blossoms fall

A useful pattern is:

• verb (plain form) + 前に = before doing / before something happens
• noun + の + 前に = before noun

Examples:

• 寝る前に = before sleeping
• 食事の前に = before the meal

In this pattern, に marks the time point connected to the main action.

So:

• 桜が散る前に、花見をしたいです = I want to do hanami before the blossoms fall

With 前に, the に is normally included in standard Japanese.

Here, と means with.

• 友達と花見をしたいです = I want to do hanami with my friend/friends

The particle と can mean different things depending on context:

• AとB = A and B
• 友達と行く = go with a friend
• 友達と花見をする = do hanami with a friend

So in this sentence, it marks the person you are doing the activity with.

It can mean either friend or friends. Japanese nouns usually do not change form for singular vs. plural.

So 友達と could mean:

• with a friend
• with friends

If the speaker wanted to be more explicit, they could add context or use something like:

• 友達みんなと = with all my friends
• 一人の友達と = with one friend

花見 literally means flower viewing, but in everyday Japanese it usually refers specifically to cherry-blossom viewing.

So when Japanese people say 花見, they often mean:

• going out during cherry blossom season
• looking at the blossoms
• often having a picnic, chatting, eating, and drinking under the trees

So it is more than just looking at flowers; it often refers to the whole seasonal activity.

The する is built into したい.

Here is the breakdown:

• 花見をする = to do hanami
• する becomes したい = want to do
• so 花見をしたい = want to do hanami

This is the same pattern as:

• 勉強をする → 勉強をしたい
• 買い物をする → 買い物をしたい

So したい is basically the want to do form of する.

Because 花見 is the thing being done.

• 花見をする = do hanami
• 花見をしたい = want to do hanami

So を marks the object of する / したい.

You may also learn that with たい, the thing wanted is sometimes marked with が instead of を:

• 寿司が食べたい
• 寿司を食べたい

Both can be natural, with some nuance differences. In this sentence, 花見をしたい is a normal and straightforward way to say it.

Because Japanese often omits subjects when they are understood from context.

So even though English needs I want to..., Japanese often just says:

• 花見をしたいです

and the listener understands that the speaker means I want to do hanami.

If you wanted to include I, you could say:

• 私は桜が散る前に、友達と花見をしたいです。

But very often 私は is omitted because it is already obvious.

たい expresses the desire, and です adds politeness.

• 花見をしたい = plain / casual
• 花見をしたいです = polite

So the sentence is in polite style because of the final です.

This is very common in everyday speech.

It comes from a verb, but たい behaves a lot like an い-adjective.

That is why you get forms like:

• したいです
• したくないです
• したかったです

So even though the meaning is want to do, the grammar of たい is adjective-like.

That is one reason learners sometimes find it a little confusing at first.

It works as a time phrase for the main action.

Structure:

• 桜が散る前に = before the cherry blossoms fall
• 友達と花見をしたいです = I want to do hanami with my friend/friends

So the whole sentence is:

• Before the cherry blossoms fall, I want to do hanami with my friend/friends.

Japanese often puts time expressions before the main clause like this.

It is natural. A few other natural versions are also possible, depending on nuance.

For example:

• 桜が散る前に、友達と花見がしたいです。
• 桜が散る前に、友達とお花見をしたいです。
• 桜が散る前に、友達と花見に行きたいです。

Small differences:

• お花見 is a more polite/common version of 花見
• 花見に行きたい focuses more on going to hanami
• 花見をしたい focuses on doing/holding hanami as an activity

So the original sentence is fine, but there are several natural alternatives.

A natural reading is:

さくら が ちる まえ に、ともだち と はなみ を したい です。

Breakdown:

• 桜 → さくら
• 散る → ちる
• 前 → まえ
• 友達 → ともだち
• 花見 → はなみ

This is useful because several of the kanji have readings that may not be obvious at first.

The comma is just marking a pause after the time phrase:

• 桜が散る前に、 ...

Japanese punctuation is somewhat flexible, and this comma helps readability. It is especially common after a longer phrase at the beginning of a sentence.

The sentence could sometimes be written without the comma, but using one here is very normal.