Slovak locale code is sk_SK.
http://wordpress.org/support/topic/wrong-locale-for-slovak
http://codex.wordpress.org/WordPress_in_Your_Language#Slovak_.E2.80.93_Sloven.C4.8Dina_.28sk_SK.29

git-svn-id: https://plugins.svn.wordpress.org/bogo/trunk@810190 b8457f37-d9ea-0310-8a92-e5e31aec5664