There's an encoding issue, so that the str_ireplace() doesn't match the word. I can't figure out how to encode your word so that it will match, but I have a different suggestion: use the existing censoring and add the word only for the given user by using a plugin on hook global_bootstrap_init_start and code like this:
PHP Code:
if ($vbulletin->userinfo['userid'] == XX)
{
$vbulletin->options['censorwords'] .= "\nحازم";
}
This is different because it will replace the word with a lot of '*' characters instead of deleting it, and also it will work everywhere the censor works instead of just for posts (which may or may not be an advantage for you).
If you'd rather not using the censoring mechanism, there are probably other hooks that can be used with MarkFL's code which will do the str_ireplace after the message text has been decoded.