Estudio japonés.

Because Spanish often drops subject pronouns when the verb already makes the subject clear.

Here, estudio is the yo form of estudiar, so Estudio japonés already means I study Japanese.

You could say Yo estudio japonés, but that usually adds emphasis, such as:

• Yo estudio japonés, no chino.
• I study Japanese, not Chinese.

Without emphasis, leaving out yo is more natural.

Estudio is the first person singular present indicative form of estudiar.

So:

• estudio = I study / I am studying
• estudias = you study
• estudia = he/she studies

In this sentence, estudio is a verb, not a noun.

Yes. Estudio can also be a noun meaning things like studio, study, or study room, depending on context.

But in Estudio japonés, it is clearly a verb, because it is followed by the language being studied. A native speaker understands it as I study Japanese, not as a noun phrase.

In Spanish, names of languages are normally written with a lower-case letter, unlike in English.

So Spanish writes:

• español
• inglés
• japonés

not Español, Inglés, or Japonés, unless the word begins a sentence.

Historically and grammatically, it is the same form as the adjective Japanese, but in sentences like this it functions as the name of the language.

So in:

• Estudio japonés

japonés means Japanese as a language.

You will see the same pattern with other languages:

• Estudio español
• Aprendo inglés
• Hablo francés

Because after verbs like estudiar, hablar, aprender, and enseñar, Spanish normally uses language names without an article.

So you say:

• Estudio japonés
• Hablo italiano
• Aprendemos alemán

But when talking about the language as an idea or topic in general, Spanish often uses the article:

• El japonés es difícil.
• Japanese is difficult.

So:

• Estudio japonés = no article
• El japonés es interesante = article used

It can mean both, depending on context.

The Spanish present tense is often broader than the English simple present. It can express:

• a general fact or habit: I study Japanese
• a current ongoing situation: I am studying Japanese

If you want to strongly emphasise that the action is happening right now, Spanish can also use:

• Estoy estudiando japonés.

But Estudio japonés is perfectly normal and often enough by itself.

The accent mark shows where the stress falls: ja-po-NÉS.

Spanish spelling rules say that words stressed on the last syllable normally need a written accent if they end in n, s, or a vowel. Since japonés ends in s and the stress is on the last syllable, it needs the accent.

So the accent helps tell you how to pronounce it correctly.

A good approximation in Spain is:

• es-TU-dyo kha-po-NES

More precisely:

• estudio sounds roughly like es-TOO-dyo
• j in japonés is the strong Spanish j sound, like a throaty h/ch sound
• the stress in japonés is on the last syllable: -nés

In standard Peninsular Spanish, the pronunciation is approximately:

• estudio: es-TU-dyo
• japonés: kha-po-NES

Yes, but it is slightly different in nuance.

• Estudio japonés focuses on studying the language, often as a subject or course.
• Aprendo japonés focuses more on learning or acquiring it.

In many everyday situations, Estudio japonés is the more natural choice for I study Japanese. But Aprendo japonés is also correct if you want to stress the learning process.

Yes, it is completely natural in Spain.

A speaker from Spain would understand Estudio japonés immediately as I study Japanese. The main regional differences would be in pronunciation, not grammar. The sentence itself works perfectly well in Spain.