Currently the only font in Ubuntu supporting (or close enough) Hong Kong Supplementary Character Set is Uming HK. WenQuanYi was claiming it supports zh-hk, but in reality it is done with fontconfig deceiving.
In HKSCS charset definition dated 2004, there are 4941 characters. Somehow, fontconfig only checks less than half of them, around 2213 or so. WenQuanYi Zen Hei included only those checked glyphs in fontconfig to claim it's done (at least according to the latest published version dated 2010-03-12). In particular, there should have been around 1700 characters in CJK extension B. WenQuanYi only has one single glyph in this range, which is also exactly the only one checked by fontconfig for zh-hk support.
In contract, UMing HK includes 4940 out of the 4941 glyphs.
Thanks for your effort to improve Ubuntu by reporting this issue!
A discussion is going on at bug 1173571 about Chinese fonts, but I can't tell to which extent it's related to this one.
If I understand it correctly, you suggest that WenQuanYi is simply removed. Some questions:
* Should it be removed from both sans-serif and monospace?
* You mention zh-hk and zh-mo in the summary. Did you intentionally not
mention zh-tw? (Are we at all using zh-mo in Ubuntu, btw?)
* What about simplified Chinese? Are your reasons for dropping
WenQuanYi valid for zh-cn and zh-sg as well?