Manual:Extension support/1.16/ExtUpgrading

$wgExtensionAliasesFiles
The use of $wgExtensionAliasesFiles and associated Extension.alias.php files is now deprecated. The new method is to put your $specialPageAliases variable in your Extension.i18n.php file and just have a $wgExtensionMessagesFiles inclusion.

$wgNamespaceAliases
There is now a new function on Language::getNamespaceAliases introduced to replace usage of $wgNamespaceAliases. This is now critical by 1.18 with the introduction of gendered namespaces aliases which are not stored in $wgNamespaceAliases.

$wgTitle
A local title is now available from some contexts. If you have a OutputPage object (often $out) then you can retrieve the Title using OutputPage::getTitle. This is the preferred method.

Http::request
HttpRequest is a new class introduced in 1.16 that provides extra functionality thank Http::request. For some uses it is recommended. In 1.17 HttpRequest however has been to MWHttpRequest. The recommendation is to use branching logic and use MWHttpRequest when possible. You may want to still support pre 1.16 however because of different calling parameters it will be at the cost of complexity.