I must say that the idea of having everything in game represented by kanji and not reusing any characters appeals to my sense of efficiency.
Apparently that's a drop in the bucket compared to the full list of Chinese characters used by asian nations.
Unihan supports some 80,000 characters, and unless I misunderstood the article, the problem with that
is that it's still not enough. I can't find a definitive number on how many Chinese characters are currently in use overall, the estimates range between 50,000 and "
unknowable". However, if we used that system, there would be enough characters to give every dwarf in the fortress their own personal symbol and still have room left over for just about anything else.
I think the Japanese alphabet (kanji) would be a bit overkill, especially since we have to consider that each character can have 15 different colors, ignoring background colors. Many of them I also believe would be too detailed to fit nicely in low-resolution tilesets.
Cyrillic I agree would be a good start, though, and as some kind of overkill might be needed, let me suggest something like the PxPlus fonts from The Oldschool PC Font Resource. With cyrillic, greek and hebrew, plus some extra technical symbols, I would say it is pretty conclusive. It also has the upside of including most roman letter variants, so if we ever get to mod the text it would be compatible with many translation mods.
You say overkill like it's a bad thing, but you've got a point about the problem with details and resolution. The differences between chinese characters and anything derived form them can get pretty subtle in some cases, and if they can't be displayed properly we're back at square one of the "What am I looking at" issue. I was going to mention arabic, but you run into the same issues there.
I didn't know that the runic alphabet and old italic were in unicode, but that's been fixed. I think those two scripts would fit in nicely with DF's overall theme, so if we had a way of tacking those onto PxPlus, that might just be all we need.