watashi wa nihongo ga daisuki desu.

I love Japanese.

Breakdown of watashi wa nihongo ga daisuki desu.

• は: topic particle
• です: to be
• 私わたし: I

Questions & Answers about watashi wa nihongo ga daisuki desu.

How do you pronounce this whole sentence?

It’s pronounced:

わたしは にほんごが だいすきです。

In romaji:

watashi wa nihongo ga daisuki desu

• 私 → わたし → watashi
• は (topic particle) → wa
• 日本語 → にほんご → nihongo
• が → ga
• 大好き → だいすき → daisuki
• です → usually said des (the u is very weak or silent in normal speech)

Why is the particle は pronounced wa, not ha?

The character は is normally read ha, but when it is used as the topic particle, it is pronounced wa.

So:

• As part of a word:
  花 → はな → hana (flower)
• As the topic marker:
  私は → watashi wa

This is just a special rule of Japanese spelling vs pronunciation.

What exactly does は do in this sentence? Is it the subject marker?

In 私は日本語が大好きです, は is the topic marker, not the grammatical subject marker.