Correct the usage of the variable passed to `wp_install_download_language_pack()` and kill an unused local variable. Props michalzuber. Also avoid using the `$_REQUEST` superglobal in this function. See #28577.
Built from https://develop.svn.wordpress.org/trunk@29016


git-svn-id: http://core.svn.wordpress.org/trunk@28804 1a063a9b-81f0-0310-95a4-ce76da25c4cd