Added Xhosa language

A quick search for xh.po files shows that the plural formula is:nplurals=2; plural=n!=1;

This was found at the following links:
http://code.metager.de/source/xref/pidgin/po/xh.po Last-Translator: Canonical Ltd 
https://gitorious.org/ghelp/nautilus/source/3f892611ab497180fae677abd652... Last-Translator: Canonical Ltd 
https://mail.gnome.org/archives/commits-list/2012-February/msg07250.html Last-Translator: Andiswa Mvanyashe
https://github.com/GNOME/gnome-font-viewer/blob/master/po/xh.po Last-Translator: Andiswa Mvanyashe