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:
```
Accept-Language: en-US,en;q=0.8,zh-Hans-CN;q=0.7,zh-Hans;q=0.5,zh-Hant-TW;q=0.3,zhHant;q=0.2
```
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 [[ https://tools.ietf.org/html/rfc5646#section-4.6 | 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`.
Patch: https://gerrit.wikimedia.org/r/#/c/193549/