watashi wa nihongo ga dekiru.

I can speak Japanese.

Breakdown of watashi wa nihongo ga dekiru.

• は: topic particle
• 私わたし: I
• 日に本ほん語ご: Japanese (language)
• が: subject particle

Questions & Answers about watashi wa nihongo ga dekiru.

What does 私 mean, and why is it included here?

私 means “I” or “me” (the first-person pronoun). In Japanese you often drop pronouns if the context is clear, but here 私 is included to explicitly state the topic (“as for me”) or to clarify who has the ability.

Why are there two particles, は and が, in this sentence?

は marks the topic — it attaches to 私, giving “as for me.”
が marks the subject of できる, which is 日本語 (“Japanese”). When you use verbs of ability like できる, the thing you can do is marked with が instead of を.

What exactly does できる mean in this context?

できる literally means “to be able to do” or “to be possible.” With a noun like 日本語, it expresses ability or proficiency: “I am able to do Japanese,” i.e. “I can use/speak/understand Japanese.”

Why not use a verb like 話す (“to speak”) in the potential form?

You could say 日本語を話せる (“can speak Japanese”), but the more common, broader expression for language proficiency is 日本語ができる. It covers speaking, listening, reading, and writing, not just speaking.