Why does Shenhua speak Japanese?

Shenhua (aka Shen Hua aka Sha Hua aka Shen Fa) "grew up in the wilderness of China, surrounded by nature" (Wikipedia). She "has lived in Guilin her whole life" (Neoseeker).

In Shenmue II, Ryo meets her and she talks to him in accent-free Japanese (according to a friend of mine who speaks Japanese). In Shenmue I she also sings in Japanese.

Why is that?

I'm not sure, but I think her original name is Chinese. She grew up in China. She lives in China. Why does she speak perfect Japanese? Is it explained in the game? Or are there any hints?

Maybe her adoptive father taught her Japanese? Is anything known about him (yet)? Is it plausible that he knows Japanese?

Solution 1:

In yesterday’s #SaveShenmue Tweetathon, Yu Suzuki answered several questions (#YouaskYu).

The following question is not especially about Shenhua, but about all people in China. However, it’s probably fair to assume, for now, that it also applies to Shenhua.

Yu Suzuki was asked [sic]:

I always wondered how ryo , being Japanese, could communicate so easy in China. Can ryo speak Chinese?

Yu Suzuki answered:

Let's not go there...

So according to Word of God, it’s (probably) not relevant to the plot that Shenhua speaks perfect Japanese.