eki ni iku totyuu de konbini ni yorimasu.

Because 行く is modifying the noun 途中.

In Japanese, a verb in plain form can come before a noun and describe it. So:

• 駅に行く途中 = the途中 of going to the station
  more naturally: while on the way to the station

Using 行きます途中 would be ungrammatical here, because ます forms do not directly modify nouns like this.

So this pattern is:

• [verb dictionary form] + 途中 = in the middle of / on the way to doing [verb]

Examples:

• 学校に行く途中 = on the way to school
• 帰る途中 = on the way home

途中 means the middle of something, partway through, or on the way.

Its meaning depends on context:

• with movement verbs like 行く, 帰る:
  途中 often means on the way
• with other actions:
  it can mean in the middle of doing something

In this sentence:

• 駅に行く途中で = while on the way to the station

So it does not mean just a physical road or path. It means the point during an ongoing action or journey.

Here, で marks the time/situation in which the main action happens.

So:

• 駅に行く途中で = while on the way to the station
• then the main action is コンビニに寄ります = stop by a convenience store

You can think of 途中で as setting the scene:
at that point / during that process

Compare:

• 授業の途中で寝た = I fell asleep during class
• 帰る途中で友だちに会った = I met a friend on the way home

So で is not marking a location here in the simple sense of at; it marks the circumstance in which something occurs.

Because 駅に行く means go to the station.

With verbs of movement like 行く, 来る, and 帰る, に often marks the destination.

So:

• 駅に行く = go to the station
• 学校に行く = go to school

You can also often use へ instead of に:

• 駅へ行く

The difference is small here:

• に focuses a bit more on the destination
• へ focuses a bit more on direction

In many everyday sentences, both are natural.

Because 寄る commonly takes に to mark the place you stop by.

So:

• コンビニに寄る = stop by the convenience store
• 友だちの家に寄る = stop by a friend’s house

Even though English uses by in stop by, Japanese uses に with 寄る.

So the two に particles in this sentence do different jobs with different verbs:

• 駅に行く → destination of 行く
• コンビニに寄る → place where you stop by with 寄る

No. 寄ります comes from 寄る, which means to stop by, drop in, or make a brief stop.

So this sentence is not saying I go to the convenience store in the normal sense. It suggests:

• the speaker is headed somewhere else
• but will briefly stop at the convenience store along the way

That nuance is important.

Compare:

• コンビニに行きます = I go to the convenience store
• コンビニに寄ります = I stop by the convenience store

The second one implies the convenience store is not the main destination.

Japanese often leaves out the subject when it is understood from context.

So this sentence could mean:

• I stop by the convenience store on the way to the station
• He/She/They stop(s) by the convenience store on the way to the station

Without context, Japanese does not always specify who the subject is.

This is very normal. In real conversation, the listener usually knows from context who is being talked about.

寄ります is the polite form of 寄る.

Using ます makes the sentence polite and neutral, which is common in:

• textbooks
• conversation with strangers
• customer service
• formal or semi-formal situations

The plain form would be:

• 駅に行く途中でコンビニに寄る。

Both mean the same thing, but the tone is different:

• 寄ります = polite
• 寄る = plain/casual

It usually refers to a habitual action or a near-future action, depending on context.

Japanese non-past forms like 寄ります can mean:

• present/habitual: I stop by the convenience store on the way to the station
• future: I’ll stop by the convenience store on the way to the station

Context tells you which one is meant.

For example:

• if someone asks what you usually do, it sounds habitual
• if someone asks what you will do now, it sounds future

Yes, that is natural.

Both are correct:

• 駅に行く途中で
• 駅へ行く途中で

The difference is small:

• に = destination-oriented
• へ = direction-oriented

In this sentence, both work well, and many native speakers would use either one depending on preference.

Japanese often puts the background information before the main action.

So the structure is:

• 駅に行く途中で = setting/background
• コンビニに寄ります = main action

This is very natural in Japanese.

You could sometimes change the order for emphasis, but the original is the most standard and easiest form. For example:

• コンビニに、駅に行く途中で寄ります。

This is possible in some contexts, but it sounds more marked and less neutral.

So the original sentence is the best basic pattern to learn.

It is read とちゅう.

So the full sentence is:

• えき に いく とちゅう で コンビニ に よります。

Useful readings here:

• 駅 = えき
• 行く = いく
• 途中 = とちゅう
• 寄ります = よります

Usually no, not in the same way.

• 途中 is the natural word for on the way / in the middle of a process
• 中 is more general and often means in the middle of doing something

For example:

• 勉強中です = I’m in the middle of studying
• 会議中です = I’m in a meeting

But for a journey like on the way to the station, 途中 is the natural choice:

• 駅に行く途中で ✅
• 駅に行く中で ❌ unnatural here

Yes. This is a very useful pattern:

• [place] に / へ 行く途中で [some action]
• [verb] 途中で [something happens]

Examples:

• 学校に行く途中で友だちに会いました。
  I met a friend on the way to school.
• 帰る途中で雨が降りました。
  It started raining on the way home.
• 仕事の途中で電話しました。
  I called in the middle of work.

So this sentence teaches a very common structure, not just one isolated expression.