Add Serbian Language

git-svn-id: https://plugins.svn.wordpress.org/related/trunk@1011340 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fix Changelog

git-svn-id: https://plugins.svn.wordpress.org/related/trunk@1011342 b8457f37-d9ea-0310-8a92-e5e31aec5664