WordPress MU

Hellow,

I install WPMU and worked well,
I need to add other language than English,

I create folder named it languages
"wp-content/languages"
, and put language file "ar.mo" in it,
then I put in wp-config.php the and edit this line to
define ('WPLANG', 'ar');

Now as I read here it must appear langauges list at
site admin-option-Site Wide Settings
but it isn't

I dont found option th change language even I do all requrment to it,

any idea?
I use WPMU v1.3.2

Well read in the codex here if oyu missed something:
http://codex.wordpress.org/Installing_WordPress_in_Your_Language

Actually I put min in /wp-includes/languages/ and it worked fine.

I do and make sure about all steps,
there is wp-includes/languages folder now
and ar.mo file in it
and no change at my control panel about language.