I'm skipping around at the moment because
Talking about this is one of those moments where I want to give up in terror.
Another thing I wanted was for the Chinese apothecary, who speaks some English, but not very well, to make mistakes based on Chinese grammar. (His daughter translates for him when necessary.) Like, when I try to speak Spanish and I'm not sure what to say, I revert to the English order of subjects and verbs and adverbs; I'm not fluent enough to think in Spanish. (I do a little better in French, but that's possibly because of the Norman influence on English.) Now, my understanding is that "Chinese only has one basic form, used for every person and tense," and additional phrases specify who and when. So rather than have really terrible stereotypical gibberish, you sit there and think, what does he want to say in Chinese, and how would he translate that directly, if incorrectly, to English?
I also figured out which particular dialect of Chinese he would speak, based on where he lives, which in turn suggests where he immigrated from. (And which suggests what kind of food he and his daughter would cook, which was something I was too dense to realize immediately.) I also realized that Wade-Giles romanization was used from the mid-19th century until 1958, when pinyin was approved, so I'm going to need to use that instead of modern romanization. And there's a character in a different part of town who speaks a different dialect--I've lost where in my notes I figured this out, but based on notes I subsequently took, it looks like my apothecary should be from Shanghai, thus speaking the Shanghainese dialect of Wu Chinese (and possibly Mandarin as a lingua franca), whereas the other character speaks Cantonese. And many of these dialects are "mutually unintelligible," so this isn't something I can just guess on my own with a Chinese-to-English dictionary. (Which is always a bad idea anyway, regardless of the language.) Basically, I have found out enough to get myself into trouble, and I'm going to have to find someone to consult on this. Possibly a linguistics professor. These are actually supporting characters, not the primary protagonists, but you see them throughout the first novel and then the daughter becomes important, so... I have to get it right.
But I'm at a point where I can't grind to a halt and figure out the specific translations just yet. I can write the dialogue in English italics when the POV character understands it, and possibly keep a lot of it that way--which might be easier for readers anyway--but if I use any Chinese at all, I'm going to have to confirm it with someone. Later. I've done enough research (and no, not just on Wikipedia) to know what I don't know, which is the important thing at this point, I guess.