Created attachment 24321
mixture of Han glyphs from Japanese and Chiense fonts under en locale

The font order in 65-nonlatin.conf in fontconfig has many issues, and is causing more and more troubles for supporting CJK languages. Here is a summary of the problems I found:

1. mixing proprietary fonts with free fonts

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.


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

In CJK fonts, there are concepts such as Song (Mincho, Ming, or Batang), or Hei (Gothic or Dotum) correspond to sans-serif and serif font in Latin world. "Kai" is a style more or less correspond to italic or script. However, these fonts were ordered in the same way in both the serif and sans-serif blocks in 65-non-latin. The proper way should be 

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 will explain the order for CJK fonts below.


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

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. See the attached screen capture:


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 (such as the language-selector-xx in Ubuntu).


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.