There are 2500+ Chinese characters in common use, compared to 26 characters of roman alphabets. As a result, in a category page, most indexing sets consists of only one member, losing the purpose of sorting. For an example see
The community guideline recommends manually indexing pages by it's pinyin (spelling of characters by roman alphabets), that is, use the syntax [[微積分 | W ]], here 微 is spelled as "wei".
Mediawiki should do this automatically.