(In reply to comment #0)
> Created an attachment (id=24321) [details]
> mixture of Han glyphs from Japanese and Chinese fonts under en locale

Right this problem is well-known.

> In this file, "MS Gothic","SimSun","PMingLiu", "HanyiSong" and "ＭＳ 明朝"
> are proprietary fonts. As far as I know, none of the Linux distros received
> permission to use these fonts from the copyright owners of the fonts. Giving a
> higher priority to proprietary fonts will increase the user's dependency to
> them, encouraging font piracy and reduce user feedbacks for FLOSS font
> development. 
> 
> In addition, "SimSun" used to be a popular "pirate" Chinese fonts for Chinese
> Linux users about 5 years ago due to the embedded bitmaps, but in the past 4
> years, WenQuanYi project has developed high quality open-source bitmap fonts
> and sans-serif Chinese fonts, and getting far more popular than SimSun and most
> other proprietary Chinese fonts.
> 
> Also, AFAIK, "ZYSong18030" was only licensed to Redhat 9, from Zhong Yi Beijing
> Inc., and this font has no embedded bitmaps. Therefore, the user group of this
> font is quite small.

Agreed.  I think the propriety fonts should be moved to a non-free .conf file at least,
which should have lower priority than free ones.  This would be a good opportunity
to clean up 65-nonlatin.conf.

> 2. sans-serif and serif used the same font order

Agree on the idea of correcting this.

> for serif:
>   bitmap Chinese fonts (style independent) > Song/Ming > Mincho/Batang > Hei >
> Gothic/Dotum > Kai > system fallback (GNU Unifont exp.)
> 
> for sans-serif:
>   bitmap Chinese fonts (style independent) >  Hei > Gothic/Dotum > Song/Ming >
> Mincho/Batang > Kai > system fallback (GNU Unifont exp.)

I think using bitmap before outline is a bad idea for JK anyway.

I suggest having a separate switch to turn on bitmap in the fontconfig rules perhaps.

> 3. fonts with lower unicode coverage and low quality were placed in front of
> more complete and polished ones

("Quality" may be subjective - anyway CJK respective styles are too different to
allow a common shared font.)

> Japanese and Korean fonts usually contains only 6000 Han glyphs, while Chinese
> fonts, the typically charset is typically 20000. Because 65-nonlatin puts many
> Japanese fonts in front of Chinese fonts, when rendering a block of text with
> Han glyphs, one often see a mixture of Gothic, Mincho, Song and Kai glyphs,
> which looks horrible.

Nod

> I suggest to put Chinese fonts in front of Japanese/Korean fonts. When Pango
> fail to determine the Chinese text (which happens when rendering Han text under
> non-CJK locales), at least we can render the text with a consistent font
> (despite the z-variant differences). If Pango can determine the language, then,
> use language specific fontconfig rules to set the font order later

Sounds reasonable enough.

> 4. order the font based on readability
> 
> The readability of Chinese fonts is a very complex problem. It is both
> technology (screen resolution, hinting techniques etc) and fashion (font styles
> from MS and Mac strongly influences Linux users) dependent. Therefore, it is
> constantly changing. More "modern" Chinese users prefer sans-serif fonts over
> the bitmap Chinese font (65% based on a survey at Ubuntu Chinese forum, N>300),
> while some other users prefer bitmaps. In any case, non-bitmaped serif font
> (Song, maybe Kai) are not preferred for most users. The order of the fonts
> shall not only consider the license, coverage, consistency, but also the
> readability.

So how about listing sans-serif (Hei) before bitmap then?