mensetu ni ha hadena sukaato no kawari ni, zimina zubon wo haite iku tumori da.

Because the two particles are doing different jobs.

• に marks the occasion or target: for / at / in the case of the interview
• は makes that phrase the topic and often adds a slight contrast: as for the interview...

So 面接には feels like:

• When it comes to the interview...
• For the interview...

The は can also suggest contrast with other situations, such as: maybe a flashy skirt is fine normally, but for the interview, the speaker plans to dress more conservatively.

Because 派手 and 地味 are na-adjectives.

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

• 派手なスカート = a flashy skirt
• 地味なズボン = plain / subdued pants

Compare that with i-adjectives, which do not use な:

• 赤いスカート = a red skirt

So here, な is just the normal way to connect a na-adjective to a noun.

The pattern is:

• Noun + のかわりに = instead of N

So:

• スカートのかわりに = instead of a skirt

The の connects the noun to かわり.

Common examples:

• 車のかわりに電車で行く = go by train instead of by car
• コーヒーのかわりにお茶を飲む = drink tea instead of coffee

In this sentence, the speaker is choosing plain pants in place of a flashy skirt.

Here, かわりに means instead of or in place of.

So:

• 派手なスカートのかわりに、地味なズボンを... = Instead of a flashy skirt, ... plain pants ...

Be aware that かわりに can sometimes have other meanings in other contexts, such as in exchange for or on the other hand, but in this sentence it is clearly the instead of meaning.

ズボンをはいて行く literally means go wearing pants.

Breakdown:

• ズボンをはく = to put on / wear pants
• はいて行く = go in that worn state / go wearing them

This is very natural when talking about what someone plans to wear to a place.

If you said ズボンで行く, that can sometimes sound more like go in pants as a general outfit choice, which is not necessarily wrong in casual speech, but ズボンをはいて行く is more explicit and textbook-clear.

はく is the dictionary form of the verb 履く, which means to wear items on the lower body or feet, such as:

• pants
• skirts
• shoes
• socks

はいて is the te-form:

• 履く → 履いて

In this sentence, the te-form connects to 行く:

• ズボンをはいて行く
• literally: put on/wear pants and go
• naturally: go wearing pants

So the te-form is linking the actions together.

The pattern Vて行く often means go after doing V or go in the state resulting from V.

Here:

• はいて行く = go wearing (them)

The point is not just that the speaker will wear pants at some point, but that they will go to the interview dressed that way.

So 行く helps express the full idea of going to the interview in plain pants.

つもりだ means intend to, plan to, or mean to.

So:

• 行くつもりだ = I intend to go / I plan to go

In this sentence:

• ズボンをはいて行くつもりだ = I plan to go wearing plain pants

It expresses the speaker’s intention, not a completed action.

Because つもりだ attaches to the plain form of the verb.

For verbs:

• dictionary form + つもりだ for positive intention
• ない-form + つもりだ for intention not to do something

Examples:

• 行くつもりだ = intend to go
• 食べるつもりだ = intend to eat
• 行かないつもりだ = intend not to go

So 行くつもりだ is the correct form.

Because Japanese often omits the subject when it is clear from context.

So even though English usually needs something like I, Japanese does not have to say it:

• (私は) 面接には...行くつもりだ

The omitted subject is understood from the situation. In a sentence about someone’s own intention, the natural assumption is often I unless context says otherwise.

This is extremely common in Japanese.

Yes, it often can.

The particle は frequently adds a contrastive nuance, even when it is subtle. So 面接には may suggest something like:

• For the interview, though, ...
• At least for the interview, ...

This can imply:

• in other situations, the speaker might wear a flashy skirt
• but for an interview, they think plain pants are more appropriate

The contrast is gentle, not dramatic, but it is there.

Sometimes yes, but the nuance is a little different.

• 面接には focuses on for the interview / when it comes to the interview
• 面接では can sound more like at the interview or in the interview situation

In this sentence, 面接には works very naturally because the speaker is talking about what they plan to wear for that occasion.

So while a learner may see both patterns elsewhere, 面接には is a very good choice here.

Japanese nouns usually do not mark singular vs. plural the way English does.

So ズボン can mean:

• pants
• a pair of pants
• sometimes just trousers

In English, pants looks plural, but in Japanese ズボン is just a normal noun with no special plural marking.

So 地味なズボン simply means plain pants / a plain pair of pants.

A helpful breakdown is:

• 面接には = for the interview
• 派手なスカートのかわりに = instead of a flashy skirt
• 地味なズボンを = plain pants
• はいて行く = go wearing
• つもりだ = intend to / plan to

So the sentence is built like this:

For the interview, instead of a flashy skirt, I plan to go wearing plain pants.

Or more natural English:

For the interview, I plan to wear plain pants instead of a flashy skirt.