Hi I had the same problem … I have modified something and It worked for me:
First the name of the MO & PO file is clean-contact-xx_XX
I have modified the code of the file clean_contact_conf.php:
1) I have replaced the first line with:
<?php load_plugin_textdomain('clean-contact', null, basename(dirname(__FILE__)));
2) I have changed all the translated string in the document and added the “clean-contact” value like this:echo __('*string*','clean-contact')
3) I have added the translation for the “setting description”
I hope it work for you
Sorry for my bad English
Here the new code modified of the clean_contact_conf.php file:
[Code moderated as per the Forum Rules. Please use the pastebin]