$wgLang is initialized towards the end of setup; some hooks are called earlier than that and should avoid using it.
When in doubt use
$wgUser->isSafeToLoad() to check.
Often used Methods
This is not an exhaustive list, view class above to see a complete listing.
$wgLang->commaList( $list )
- delimit a list of strings according to the conventions of the user's language
- return the user's language code, for example "en"