Manual:$wgDefaultLanguageVariant

Details
Default variant code, if false, the default will be the language code. Only works when it is defined as a variant in the LanguageConverter class of that language.

Usage
$wgLanguageCode = "sr"; $wgDefaultLanguageVariant = "sr-el"; This will use Serbian system messages in Latin-script, but report for javascript the simple contentlanguage="sr".
 * In LocalSettings.php, one may set:

$wgLanguageCode = "zh"; $wgDefaultLanguageVariant = "zh-cn"; 这样设置，显示的会是大陆简体，但是会告诉javascript语言设置是"zh"
 * In LocalSettings.php, one may set: