As a generally agreed consensus among web designers and font professionals, Chinese font-family do not have italicized variations, and should have use Fangsong (semi-cursive) or Kaiti (cursive) instead when needed. The semantic web specification defined the i tag as in alternative voice, which should be reflected in how we process it. An alternative font must be used to be in compliance with respective web standard, and computer-generated italics must be replaced.
For start, tag:lang('zh') could be a path to explore. Just to clarify, we need use a different font family for the <i> tag, not font-style as Chinese font families do not have their italicized/obliqued variations, similar thing could be said for Japanese and Korean I believe.
This seems to be a rare case, if an OS support Chinese fonts, it is likely they will have the whole set (Hei, Song, Fangsong, Kai, sometimes Yuan). Windows and macOS and some major linux distributions like Ubuntu certainly do. Anyway, we can always fallback to the default 'cursive' font as specified by the system, fall back to a serif font might also be acceptable in extreme cases. There is also the web font solution, however, I believe that is outside of the scope of this issue.
- I am not sure if the Chinese font is included in the non-Chinese operating system.
- How to ensure that after the fallback to the default font, does <i> tag fallback to the default italic? Or not?
- Chinese webfont are a lot of troubles, And currently mediawiki does not have Chinese webfont solution.
- This case is not rare, many people in the Chinese-speaking area must use an English operating system for various reasons at work.