> I'm not sure what a "moderate amount of Mandarin" means; if it's on the lower end, you might be interested to know that the "other" sense does survive in Mandarin, in the words 其他 ["other"; extremely common] and 他人 ["other people"; not so common]. 他 by itself is going to be overwhelmed by the far more common use as a pronoun, I would guess.
I had a snippet about how 他 was made up of 也 and 人, "also a person", but ended up editing it out, as I wasn't sure it was actually connected w/ Japanese using it to mean "other". "他人" is still about people, but I had forgotten 其他, which is clearly not specific to people.
At any rate, there's a lot of ways our hypothetical universe could go, WRT how such a 汉字 writing system would be incorporated into English. The point is, there's always a silver lining: It would certainly have some benefits, like making it possible for literate English-speakers to get around in China and Japan w/o learning anything about the local languages and vice versa (with some of the "false friend" [1] traps you've mentioned above -- but those are issues between European languages as well).
But on the whole, I'd consider the cost not worth the benefits by a long shot.
> I had a snippet about how 他 was made up of 也 and 人, "also a person", but ended up editing it out, as I wasn't sure it was actually connected w/ Japanese using it to mean "other".
Well, I don't think it's true, either. As I understand it, the form 他 is just a graphical simplification of 佗, with no connection to the character 也. (You can think of this as similar to how the left-hand component in 脸 is 肉, not 月.) It isn't clear to me either that the character 也 would have held any sense of "also" when the form 他 appeared, though this is a question I'm agnostic on.
I've watched several videos on youtube in which someone presents Japanese people with uncommon kanji and asks them to read them, or failing that to speculate on what they might say. The Japanese unfailingly speculate that both halves of a compound character are relevant to the meaning, which surprises me - it's very rare for a character to be constructed from two meaningful parts. Far more common are the characters in which one part gestures at the meaning and the other part tells you the pronunciation, and 佗 is one of those. 从人它聲。
I had a snippet about how 他 was made up of 也 and 人, "also a person", but ended up editing it out, as I wasn't sure it was actually connected w/ Japanese using it to mean "other". "他人" is still about people, but I had forgotten 其他, which is clearly not specific to people.
At any rate, there's a lot of ways our hypothetical universe could go, WRT how such a 汉字 writing system would be incorporated into English. The point is, there's always a silver lining: It would certainly have some benefits, like making it possible for literate English-speakers to get around in China and Japan w/o learning anything about the local languages and vice versa (with some of the "false friend" [1] traps you've mentioned above -- but those are issues between European languages as well).
But on the whole, I'd consider the cost not worth the benefits by a long shot.
[1] https://en.wikipedia.org/wiki/False_friend