Sophia-senpai sometimes talks in/adds English words. I'm using a slightly different font for that, like the "see you tomorrow" at the end of chapter 9. When the change is in the same sentence, the font difference will be more obvious (there weren't any in 10). She's also doing that desu thing foreigners in anime often do, like the catgirl from No Game No Life, I think. I didn't have any idea how to reflect that though.