Renames the label to "Language" and adds an explanation of the feature to the help tab. Props johnbillion, jorbin. Fixes #38344. Built from https://develop.svn.wordpress.org/trunk@38856 git-svn-id: http://core.svn.wordpress.org/trunk@38799 1a063a9b-81f0-0310-95a4-ce76da25c4cd