Learn Hardcore Japanese: nihongo no kaiwa ga zyoutatusuru uti ni, rensyuuaite to hanasu zikan ga dondon tanosiku natte kimasita. - As my Japanese conversation improved, the time I spent talking with my practice partner became more and more fun.

の here is just linking two nouns: 日本語 (Japanese language) + 会話 (conversation), so 日本語の会話 literally means “conversation of Japanese / Japanese-language conversation.” In natural English: “conversation in Japanese.”

Some contrasts:

日本語の会話
- Very natural, neutral.
- Focuses on “conversation in Japanese” as a general ability or activity.
- E.g. 日本語の会話が上達する = “(my) Japanese conversation (skills) improve.”
日本語会話
- Noun compound; you often see it in titles: textbook names, course names, etc.
- Feels a bit more “label-like” than how you’d usually talk in a sentence.
- E.g. 日本語会話クラス = “Japanese conversation class.”
日本語での会話
- Uses で to show the means / medium (“by means of Japanese”).
- Slightly more formal or explicit: “conversation conducted in Japanese.”
- Very common in writing or when you want to emphasize the language used.

In this sentence, 日本語の会話 is the most natural, everyday way to say “Japanese conversation (as a skill / activity).”

Why is it 会話が上達する and not 会話を上達する? What does が mark here?

上達する means “to improve / to get better” and it’s an intransitive verb in Japanese.
The thing that improves is the subject, so it takes が, not を:

会話が上達する
“Conversation (skills) improve.”

You can’t say × 会話を上達する, because that would treat 上達する like a transitive verb (“to improve something”), which it is not.

Compare:

日本語が上達した。
“My Japanese has improved.”
ギターが上達した。
“My guitar (playing) has improved.”

In this sentence, 日本語の会話が上達するうちに =
“as my Japanese conversation (ability) improved”, with 会話 as the grammatical subject marked by が.

What does うちに mean in 上達するうちに? How is it different from 間（あいだ）?

Here 〜うちに means “as / while / over the course of (something happening or changing)”.

So:

日本語の会話が上達するうちに
≈ “as my Japanese conversation improved / while it was improving / over the process of it improving”

Difference from 間（あいだ）:

〜間（あいだ） often emphasizes a time span during which something continues:
- 映画を見ている間、静かにしてください。
  “Please be quiet while we’re watching the movie.”
- Action/state continues for that whole stretch.
〜うちに here emphasizes a natural change that happens during that period:
- 日本語の会話が上達するうちに、〜
  “As my Japanese conversation was (gradually) improving, 〜 happened.”
- The improvement and the other change (conversation becoming fun) are linked.

So うちに in this sentence gives a feeling of gradual, natural development over time, rather than just a neutral time span.

Where is the subject “I” in this sentence? Why isn’t 私 written?

Japanese often drops the subject when it’s clear from context. In English you must say “I / you / he / she…”, but in Japanese it’s very natural to leave it out.

In this sentence:

日本語の会話が上達するうちに、練習相手と話す時間がどんどん楽しくなってきました。

A natural English translation is:

“As my Japanese conversation improved, the time I spent talking with my practice partner became more and more fun.”

The “I” is understood from context and from the use of 〜てきました, which often implies the speaker’s own experience. If you really want to say it explicitly, you could say:

私は日本語の会話が上達するうちに、〜

but in normal Japanese it’s usually omitted unless needed for clarity or contrast.

What does 練習相手と話す時間 literally mean? Why do we need 時間 here?

Break it down:

練習相手 – practice partner
と – with
話す – (I) talk
時間 – time

In Japanese, a plain-form clause can directly modify a noun:

練習相手と話す時間
= “time [when/that I] talk with my practice partner”
≈ “the time spent talking with my practice partner”

Using 時間 makes it clear we’re talking about the period of time, not just the act abstractly.

Compare:

練習相手と話すのが楽しい。
“Talking with my practice partner is fun.”
練習相手と話す時間が楽しい。
“The time (I spend) talking with my practice partner is fun.”

The sentence uses the second pattern, focusing on the time itself becoming more enjoyable.

What does どんどん mean here, and why is it before 楽しく?

どんどん is an adverb meaning things like:

“more and more”
“steadily / rapidly / continuously”

It adds the idea of ongoing or increasing change.
So:

どんどん楽しくなってきました。
≈ “It became more and more fun.”
(Not just “became fun” once, but increasingly fun.)

Position: in Japanese, adverbs normally come before the verb or adjective phrase they modify. Here:

どんどん modifies 楽しくなってきました, so it goes right in front of 楽しく.

You could also put it at the start of the second clause for a slight shift in emphasis:

日本語の会話が上達するうちに、どんどん練習相手と話す時間が楽しくなってきました。

Meaning is basically the same: it still describes the degree of “fun” increasing.

Why is it 楽しくなってきました and not 楽しい or 楽しかったです?

楽しい is an i-adjective (“fun / enjoyable”).
To express “become ~”, Japanese uses:

i-adjective (stem) + く + なる
e.g. 楽しい → 楽しくなる = “to become fun”

So:

楽しくなりました。 – “It became fun.”
楽しくなってきました。 – “It has (gradually) become fun (up to now).”

If you said just:

楽しいです。 – “It is fun.” (state, no sense of change)
楽しかったです。 – “It was fun.” (past state, no story of development)

In this sentence, the speaker wants to express a change over time linked to improvement in Japanese, so they use:

楽しく (the く-form of 楽しい)
- なる (“become”)
in 〜てくる form (なってきました) to show that this change has progressively happened up to now.

So 楽しくなってきました = “It has become more and more fun (recently / over that period).”

What extra nuance does 〜てくる add in 楽しくなってきました compared to 楽しくなりました?

Both express a change, but:

楽しくなりました。
- “It became fun.”
- A change that happened (or is viewed) as a simple fact in the past.
楽しくなってきました。
- Uses 〜てくる, which often means:
  - a change started in the past
  - and has continued up to the present point.
- Nuance: “has come to be fun / has grown to be fun.”

In this sentence:

…練習相手と話す時間がどんどん楽しくなってきました。

The idea is:

At first it maybe wasn’t so fun (because of limited Japanese).
Over time, as the Japanese conversation improved,
the time spent talking gradually became (and is now) fun.

So なってきました nicely matches どんどん and 〜うちに, giving a picture of continuous, cumulative change leading up to now, not just a single moment of “it became fun.”