Language file not working

I have a plugin that I made for comment spam:

http://plugins.svn.wordpress.org/comment-redlist/

Somebody emailed me and asked if they could translate it to Spanish, and I of course said yes. They sent me a pot file and an mo file. I put them in my languages directory, which I called “localization”. The only way I know to test is to change WPLANG in wp-config.php, but when I do that the plugin does not show the Spanish text.

I did add WordPress’ Spanish mo files, so the rest of WordPress is showing Spanish text, but for some reason my plugin isn’t.

load_plugin_textdomain() is called on line 187 of comment-redlist.php.
The mo file is named comment-redlist-es_ES.mo, and the pot file is named comment-redlist-es_ES.pot.

Maybe I just don’t know how to test this right, but if somebody can let me know I’d appreciate it.