Learn Hardcore Japanese: watasi ha nihongo no syousetu wo mutyuu ni yomimasita. - I read a Japanese novel, completely absorbed in it.

私 (わたし) – “I / me”
は – topic marker: “as for / speaking of ”
日本語 (にほんご) – the Japanese language
の – connects 日本語 to 小説; makes “Japanese-language _”
小説 (しょうせつ) – novel / fiction
を – object marker: marks 日本語の小説 as what was read
夢中 (むちゅう) – “absorption, being engrossed, being crazy about something”; a noun / na-adjective
に – turns 夢中 into an adverbial (“in an absorbed way”)
読みました (よみました) – polite past form of 読む “to read”: “read”

So the structure is:
[topic] 私は [object] 日本語の小説を [manner] 夢中に [verb] 読みました。

Why is は used after 私 and not が?

は marks the topic of the sentence, not just the grammatical subject.

私が日本語の小説を夢中に読みました。
– Emphasizes who did it, often in contrast to someone else: “I (as opposed to someone else) read…”
私は日本語の小説を夢中に読みました。
– “As for me, I read a Japanese novel, absorbed in it.”
– Neutral, just introducing “me” as what we’re talking about.

In a sentence like this, where there is no strong contrast or focus on “who,” Japanese usually prefers は. Using が here sounds like you’re answering a “who?” question or contrasting yourself with others.

Would native speakers normally say 私 here, or would they drop it?

In natural conversation, 私 is very often dropped when it’s obvious who the subject is.

So all of these are possible:

私は日本語の小説を夢中に読みました。 – Explicit “I”; fine, a bit more formal/bookish.
日本語の小説を夢中に読みました。 – Most natural if context already makes it clear that you’re talking about yourself.

Pronouns like 私 are used far less than English “I,” especially when the subject is already known from context.

What exactly does 日本語の小説 mean? Is it a novel about Japanese, or written in Japanese?

日本語の小説 normally means:

“a novel written in Japanese (the language)” or “a Japanese-language novel.”

It does not usually mean “a novel about the Japanese language.” For that you’d say something like:

日本語についての小説 – a novel about the Japanese language
日本語学に関する小説 – a novel related to Japanese linguistics (very specific)

Without extra explanation words like について, X語の小説 almost always refers to the language it’s written in (英語の小説 = a novel in English, etc.).

What is the function of の in 日本語の小説? Is it just possession?

の here is a general modifier connector. It’s broader than simple possession.

It can show many relations, including:

possession: 田中さんの本 – Tanaka’s book
type / category: 日本語の小説 – a Japanese-language novel (type)
origin: フランスのワイン – wine from France
material: 木の机 – a desk made of wood

So 日本語の小説 is “a novel of (the category) Japanese language,” i.e. “Japanese-language novel,” not “Japanese language’s novel” in a literal possessive sense.

Could I say 日本語で小説を… instead of 日本語の小説を…? What’s the difference?

Yes, you can say both, but the nuance is different:

日本語の小説を夢中に読みました。
- Focus: what kind of novel it is.
- Meaning: “I read a Japanese-language novel (or novels), absorbed in it.”
日本語で小説を夢中に読みました。
- 日本語で = “in Japanese” as the means/language used.
- This sounds like: “I read a novel in Japanese, absorbed in it.”
- It doesn’t tell us what language the novel is originally in; it just says you used Japanese to read it (which usually implies it’s Japanese, but grammatically that’s not the focus).

General pattern:

Xの本 / Xの小説 → a book/novel of type X (e.g., language, genre, etc.)
Xで読む / Xで話す → read/speak in X (X = language used for the action)

What kind of word is 夢中, and what does 夢中に do grammatically?

夢中 (むちゅう) is both:

a noun (“absorption, trance-like focus”), and
a na-adjective (“absorbed, obsessed, crazy about”).

As a na-adjective, you can make it adverb-like by adding に:

夢中に読む – “to read in an absorbed way / engrossed in reading.”

This follows the regular pattern:

静か（な） → 静かに話す – speak quietly
きれい（な） → きれいに書く – write neatly
夢中（な） → 夢中に読む – read in an absorbed way

So 夢中に in the sentence is an adverbial phrase describing the manner of reading.

I often see 夢中で or 夢中になって. Is 夢中に読みました natural, and what’s the difference among に, で, and になって?

All three are grammatically possible, but there are preference differences:

夢中に読む / 夢中に読みました
- Adverbial に from the na-adjective.
- Means “to read in an absorbed way.”
- Correct Japanese, but in everyday speech, many native speakers more often say 夢中で or 夢中になって with 読む.
夢中で読む / 夢中で読みました
- で = “in the state/condition of …”
- Very common collocation: 本を夢中で読む.
- Nuance: “I read while being in a state of absorption.”
夢中になって読む / 夢中になって読みました
- Literally: “having become absorbed, (I) read.”
- Very natural and vivid: “I got really into it and read.”

So:

Your sentence with 夢中に is grammatically fine.
For the most natural-sounding phrase in conversation or writing, 夢中で読みました or 夢中になって読みました is probably more typical.

Why does the object marker を come before 夢中に instead of right before 読みました?

In Japanese, particles attach to the word/phrase they mark, not to the verb.

Here, を belongs to the object noun phrase:

日本語の小説 (Japanese-language novel) + を (object marker)

Then you can insert adverbs or adverbial phrases (夢中に) between the object and the verb:

日本語の小説を夢中に読みました。
日本語の小説をゆっくり読みました。 – read a Japanese novel slowly

The particle doesn’t have to be immediately next to the verb; it just has to be attached to the correct noun phrase.

Can I change the word order, like 私は夢中に日本語の小説を読みました? Does that change the meaning?

You can change the order somewhat, and the basic meaning stays the same, but the focus and naturalness can shift.

Possible versions:

私は日本語の小説を夢中に読みました。
– Very natural. Neutral order: topic → object → manner → verb.
私は夢中に日本語の小説を読みました。
– Also possible. Slightly more focus on how you read (夢中に).
– “I, absorbed, read Japanese novels.”
日本語の小説を私は夢中に読みました。
– Emphasizes 日本語の小説 as contrastive (“As for Japanese novels, I read them absorbedly”).

In Japanese, word order is fairly flexible, but the most common in this case is the original:
私は日本語の小説を夢中に読みました。

What level of politeness is 読みました, and how would it look in casual speech?

読みました is the polite past form of 読む.

Polite past: 読みました
Plain/casual past: 読んだ

So in casual speech with friends, you’d probably say:

日本語の小説を夢中に読んだ。
(Often also dropping 私は.)

Formality scale (same meaning):

日本語の小説を夢中に読んだ。 – casual
日本語の小説を夢中に読みました。 – polite / standard

How do I say that I was in the middle of reading, not that I simply read (and maybe finished)?

読みました just states a past action; it often implies completion, like “I read it (through).”

To emphasize an ongoing past action, you can use the progressive:

日本語の小説を夢中で読んでいました。
– “I was absorbed in reading a Japanese(-language) novel.”
– Focuses on the state of being in the middle of reading.

You can also say:

日本語の小説を夢中になって読んでいました。
– “I was engrossed in reading Japanese novels.”

How do I show that I’m talking about multiple novels instead of just one, since 小説 has no plural marker?

Japanese usually leaves number to context, so 小説 can mean:

“a novel,” “the novel,” or “novels” in general.

If you really want to emphasize plurality, you can:

Use a quantity:
- 日本語の小説をたくさん夢中に読みました。
  – “I read many Japanese(-language) novels, absorbed in them.”
- 日本語の小説を何冊も夢中に読みました。
  – “I read several (many) Japanese novels, absorbed in them.”
Use a phrase like いろいろな小説:
- いろいろな日本語の小説を夢中に読みました。
  – “I read various Japanese novels, really absorbed.”

Without such markers, 小説 on its own is intentionally number-neutral.