[trunk] - Language_switch

git-svn-id: http://piwigo.org/svn/trunk@21992 68402e56-0260-453c-a942-63ccdbb3a9ee
[trunk_admin] Update sl_SI, thanks to : simon.krajnc

git-svn-id: http://piwigo.org/svn/trunk@21999 68402e56-0260-453c-a942-63ccdbb3a9ee