Learn Hardcore Japanese: nihongo ha watasi no itiban no syumi desu.

は marks 日本語 as the topic:
- 日本語は私の一番の趣味です。
  → “As for Japanese, it is my number one hobby.”
- This sounds like you are talking about Japanese in general and giving information about it.
が marks 日本語 more strongly as the focus or answer:
- 私の一番の趣味は日本語です。
  Here, が is not natural; we use は with the topic.
- But in something like 一番の趣味が日本語です, you are emphasizing what the hobby is (e.g., in contrast to other options).

With the exact word order you gave:

日本語が私の一番の趣味です is possible, but it sounds like you’re specifically identifying Japanese as the thing that fills the role of “my top hobby,” often in a context of contrast or correction.
In everyday neutral speech, 日本語は私の一番の趣味です is more natural.

Can I change the word order to 私の一番の趣味は日本語です? Is that more natural?

Yes, 私の一番の趣味は日本語です is very natural and extremely common.

日本語は私の一番の趣味です。
→ Topic: 日本語 (Japanese)
→ Comment: it is my top hobby.
私の一番の趣味は日本語です。
→ Topic: 私の一番の趣味 (my number one hobby)
→ Comment: it is Japanese.

Both mean the same thing overall. The difference is which part is highlighted as the topic:

If you are talking about your hobbies, 私の一番の趣味は日本語です flows very naturally.
If you are talking about Japanese, 日本語は私の一番の趣味です fits well.

Why are there two の particles in 私の一番の趣味? What does each の do?

The structure 私の一番の趣味 breaks down like this:

私の → “my”
- 私 (I) + の = “of me” → my
一番の趣味 → “number one hobby / favorite hobby”
- 一番 = “number one / the most”
- 一番の趣味 literally = “hobby that is number one”

Putting it together:

私の (一番の趣味) = “my (number one hobby)”

This kind of “double の” is very common in Japanese:

日本の歴史の本 = a book of Japanese history
彼の好きな音楽 (here a な, but similar nesting idea) = the music he likes

Each の just links one noun (or noun-like word) to the next.

Can I drop 私の and just say 日本語は一番の趣味です?

Yes, you can say 日本語は一番の趣味です, and it is grammatically correct.

Japanese often omits 私 (“I / my”) when it is clear from context that you’re talking about yourself.
In a conversation about your hobbies, people will naturally understand that 一番の趣味 refers to your number one hobby.

However:

日本語は私の一番の趣味です explicitly says “my number one hobby,” which can sound a bit clearer or more emphatic, especially in standalone sentences or writing.

What exactly does 一番 mean here? Is it “the best,” “most,” or “favorite”? Why is there a の after it?

一番 (いちばん) literally means “number one.” Its meaning depends on how it’s used:

Before adjectives, it works like “most”:
- 一番高い = tallest / most expensive
- 一番好き = like the most
Before a noun with の, it works like “number one / top / favorite”:
- 一番の友達 = best friend / number one friend
- 一番の趣味 = top hobby / number one hobby → effectively “favorite hobby”

The の here turns 一番 into something like a descriptor of the noun:

一番の趣味 = “the hobby that is number one (for me).”

So in context, 私の一番の趣味 is naturally understood as “my favorite hobby.”

What is the nuance of 趣味 (しゅみ)? Is it the same as “something I like,” or is it more like an actual hobby?

趣味 usually means “hobby,” but the nuance is:

It suggests something you:
- do repeatedly or regularly,
- enjoy in your free time,
- somewhat “identify with” as a personal interest.

Examples:

私の趣味は読書です。 = My hobby is reading.
趣味で写真を撮っています。 = I take photos as a hobby.

It’s not the same as just “liking” something:

日本語が好きです。 = I like Japanese. (You enjoy it.)
日本語は私の趣味です。 = Japanese is my hobby. (You pursue it like a hobby, e.g., study, read, watch things in Japanese.)

So 日本語は私の一番の趣味です implies that learning/using Japanese is your main hobby activity, not just something you vaguely like.

Why doesn’t the sentence use を, like 日本語を私の一番の趣味です?

を marks the direct object of an action verb, like:

日本語を勉強します。 = I study Japanese.
映画を見ます。 = I watch a movie.

But in 日本語は私の一番の趣味です, the verb です is a copula (“to be”), not an action verb:

Structure: A は B です
→ A is B.

So:

日本語 = A (topic)
私の一番の趣味 = B (what A is)
です = “is”

There is no direct object here, so を would be incorrect.

Why is は pronounced “wa” in 日本語は? I thought は is “ha.”

This is one of the quirks of Japanese:

The character は is normally read “ha” in words:
- はな = hana
- はやい = hayai
But when は is used as the topic particle, it is pronounced “wa.”
- 日本語は → にほんご wa
- 私は学生です。 → わたし wa がくせいです。

So the rule is:

Spelling: always write the particle as は
Pronunciation (when particle): wa

This is just a conventional spelling that learners have to memorize.

What politeness level is です here? Could I say 日本語は私の一番の趣味だ instead?

です is the standard polite form of “to be.”

日本語は私の一番の趣味です。
→ Polite, appropriate for most situations (talking to strangers, teachers, coworkers, etc.).
日本語は私の一番の趣味だ。
→ More casual / plain form, typical in:
- talking to close friends or family,
- monologue (novels, inner thoughts),
- diary-like writing.

Grammatically both are correct. Use:

です when you want to be polite or neutral.
だ when you are in a casual setting and your overall speech is casual (using だ, ～よ, ～じゃない, etc.).

Can 日本語 here mean “Japanese culture” in general, or does it strictly mean the Japanese language?

In this sentence, 日本語 specifically means “the Japanese language.”

語 means “language” (as in 英語 = English, 中国語 = Chinese).
So 日本語 = the Japanese language.

If you want to talk more broadly about “Japan/Japanese things” as a hobby, you would use other words, for example:

日本文化 (Japanese culture)
日本のこと (things about Japan)
日本のアニメや漫画 (Japanese anime and manga), etc.

So 日本語は私の一番の趣味です is understood as:

“Studying/using the Japanese language is my number one hobby.”

Is there a difference between 日本語は私の一番の趣味です and 日本語は私の趣味です?

Yes, the nuance is different:

日本語は私の趣味です。
→ “Japanese is my hobby.”
→ Implies it’s a hobby of yours, but doesn’t say whether it’s the top one.
日本語は私の一番の趣味です。
→ “Japanese is my number one hobby / my favorite hobby.”
→ Clearly marks Japanese as your top hobby, above other hobbies you might have.

So 一番の adds the idea of ranking: it’s not just “a hobby,” it’s your number one.

How do you read the whole sentence in romaji, and which word is stressed in natural speech?

The sentence 日本語は私の一番の趣味です。 is read:

にほんごはわたしのいちばんのしゅみです。
Romaji: Nihongo wa watashi no ichiban no shumi desu.

In natural speech:

Content words carry more stress: にほんご, わたし, いちばん, しゅみ.
Particles (は, の) and です are usually lighter and shorter.

There isn’t “word stress” like in English, but you would typically give a bit more emphasis to:

にほんご if you’re focusing on Japanese, or
いちばん / しゅみ if you’re emphasizing how much it is your top hobby.

Could I say something like 日本語を勉強することは私の一番の趣味です instead? How is that different?

Yes, 日本語を勉強することは私の一番の趣味です is correct and natural.

日本語は私の一番の趣味です。
- Literally: “Japanese is my number one hobby.”
- It’s slightly abstract—“Japanese” stands for the whole activity of learning/using it.
日本語を勉強することは私の一番の趣味です。
- Literally: “Studying Japanese is my number one hobby.”
- This explicitly states that studying Japanese is the hobby.

In many contexts, both will be understood the same way; the second one just spells out the action more clearly.