Language setting like these,
$wgLanguageCode = "zh";
$wgDefaultLanguageVariant = "zh-cn";
$wgDisabledVariants = array( 'zh-hans', 'zh-hant', 'zh-hk', 'zh-mo', 'zh-my', 'zh-sg' );
and currently, only user set their language to zh-cn, zh-tw show correct time in local language. All other zh & zh-xx setting will show English time.