Touhou Headcanons

Satori and Koishi

Due to the fact that some people, even in Gensokyo, might not have Japanese as their first language and might think in other languages, satori are taught from an early age to be able to speak and understand several different languages, so they can read the minds of even those who do not think in Japanese.

Because of this, Satori and Koishi both speak a variety of languages. (Keep in mind, Koishi was taught to speak all those languages before she closed her third eye, back when she could still read minds.) Occasionally, when they do not want to be overheard, Satori and Koishi will have conversations in another language.

However, due to her forgetful nature, Koishi still has trouble with certain words and terms in languages other than her native Japanese, so when conversing with someone in, say, English, it takes her a while to remember certain words and phrases. For instance:

Koishi: So, I went and asked Meiling if I could borrow, uhhhh, the, um, the thing.
Someone else: The "thing?"
Koishi: Yeah, that thing with the little... (under her breath) Sono koto no namae wa nanidesu ka.... THE FISHING ROD!

Bonus: At one point when Koishi was visiting her best friend Flandre, Koishi pleasantly surprised her by talking to her in French, which, by the way, is Flandre's native language. (Recall that I headcanon the Scarlet sisters to be French.) Koishi repeatedly apologized for all the slip-ups and grammatical errors she made, but Flandre said it was okay and she was glad that Koishi was trying and impressed by the fact that she even knew French in the first place.