Manual:Extension support/1.13/ExtUpgrading

SpecialPage localization
There is now a new variable to set up SpecialPage localization in Extensions. While the $specialPageAliases variable has existed since 1.9 it only now has been available to extension authors. Point $wgExtensionAliasesFiles to load a Extension.alias.php file. It may be that you will want to copy your messages to $aliases, the precursor to $specialPageAliases in case any core code has not been converted yet.