Currently, Chinese language converter only supports these language codes: zh, zh-hans, zh-hant, zh-cn, zh-sg, zh-my, zh-hk, zh-mo, and zh-tw. The Accept-Language header field sent by IE 11 on Windows 8.1 is something like:
The result is that MediaWiki doesn't recognize zh-Hans-CN, so zh-Hans is used, which is less desirable than zh-cn. Also according to RFC 5646 Section 4.6, zh-Hans-CN is preferred over zh-cn.
A tag such as "zh-Hans-XQ" conveys a great deal of public, interchangeable information about the language material (that it is Chinese in the simplified Chinese script and is suitable for some geographic region 'XQ').
So I propose to add zh-hans-cn to variantfallbacks array in LanguageZh.php.