Hello, I saw that you have already translated the plugin, but I don't know why it's not in the zip's plugin.
I've downloaded the spanish mo to a new folder /languages/ and upload it.
I changed the line 38 from wp-postratings.php to:
load_plugin_textdomain('wp-postratings', false, dirname(plugin_basename(__FILE__)).'/languages/');
but it doesn't work.