Manual:$wgExtraLanguageCodes/zh

细节
该数组使代码不会在安装程序上显示为可选语言，并在运行脚本时将其排除在外.

In, the variable is created by combining these codes with a list of "deprecated" codes, which are mostly leftovers from renames or other legacy things, and the internal codes 'qqq' and 'qqx'.

A mapping in  takes precedence over built-in mappings.