.po, .mo translation files are ignored

Hey, sorry to bother you guys again. For some reason I can't get the translation files for Private Messaging to take effect.

I tried it with the German translation available on your website, i also tried to create my own... I put the files in the wp-content/plugins/languages directory, also tried putting it directly in private-messaging/languages.

My wordpress installation is set to German. I also tried inlcuding define ('WPLANG', 'de_DE'); directly in wp-config. Yet none of this has helped so far.

The translation files are named "private-messaging-de_DE".
Any help would be appreciated.