first u need to install Arabic fonts
u can use Microsoft true font
# yum install cabextract
# wget
http://fontconfig.org/webfonts/webfonts.tar.gz
# tar xvfz webfonts.tar.gz
# cd msfonts
# cabextract *.exe
# mkdir /usr/share/fonts/microsoft
# cp *.[tT]* /usr/share/fonts/microsoft
# cd ..
# rm -fr msfonts
# fc-cache
second from system > preferences > hardware > keyboard
choose layouts tab
add >> arabic
ok
u can change languages by pressing the 2 Alt buttons at the same time
also u can add a keyboard language indicator in the menu bar by
right click >> add to panel >> keyboard indicator
thats all , hope i give some hand...