I look better into it and I was wrong! Unfortunately you have to change the languge module php code. The problem is that the language module pools languages name from the configuration.php file. But if you change the configuration file so that instead of persian to return فارسی the module will not work at all.
So replace lines 221-227 of /modules/mod_language.php file to this:
if ($langx == 'persian') {
$persianlang = 'فارسی';
echo '<a href="'.$link.'" title="'.$persianlang.'">';
if (($this->lng_style == 0) && file_exists($mainframe->getCfg('absolute_path').'/language/'.$langx.'/'.$langx.'.gif')) {
echo '<img src="'.$mainframe->getCfg('ssl_live_site').'/language/'.$langx.'/'.$langx.'.gif" border="0" alt="'.$persianlang.'" style="vertical-align:middle" />';
} else {
echo ($lang == $langx) ? '<strong>'.$persianlang.'</strong>' : $persianlang;
}
echo '</a> '._LEND;
} else {
echo '<a href="'.$link.'" title="'.$langx.'">';
if (($this->lng_style == 0) && file_exists($mainframe->getCfg('absolute_path').'/language/'.$langx.'/'.$langx.'.gif')) {
echo '<img src="'.$mainframe->getCfg('ssl_live_site').'/language/'.$langx.'/'.$langx.'.gif" border="0" alt="'.$langx.'" style="vertical-align:middle" />';
} else {
echo ($lang == $langx) ? '<strong>'.$langx.'</strong>' : $langx;
}
echo '</a> '._LEND;
}
I cannot test it, but I think that this will work for you...