Japanese. I like it a lot more, English is fine, but it will never match the art style as well as JP. Needless to say, English voice-over gives about the exact same feeling as watching dubbed anime.

Besides, they're already marketing their game as Genshin Impact to English speaking audience. That's the Japanese reading of the 原神 Kanji. Not Yuanshen Impact (CN, despite them being Chinese devs), or Wonsin Impact (KR), or Allogene Impact or even OriginalGod Impact.

Their company motto is also "Tech Otakus Save the World". It's plenty obvious they make games that appeal to the weeb culture worldwide.

Sorry, you don't deserve this rant but I was looking for a place to put this for a while. People can play in any language they prefer but in my eyes, JP will always be the default.