@mc_jesse, I think the OP already has their WordPress language defined and configured properly, since the back end is in french on his/her install.
@nohant, the problem you're looking stems from the plugin trying unsuccessfully to load a language (.mo) file from its /po/ directory. Open up mailchimp.php in your /plugins/mailchimp directory; around line 58, you'll see this bit of code:
function mailchimpSF_plugin_init() {
// Internationalize the plugin
load_plugin_textdomain( 'mailchimp_i18n', MCSF_DIR.'po/');
This is the bit that tells the plugin to load up the appropriate language file based on your WordPress installation language. It seems it can't find the right directory in some cases though. Just change it to:
function mailchimpSF_plugin_init() {
// Internationalize the plugin
load_plugin_textdomain( 'mailchimp_i18n', false, dirname(plugin_basename( __FILE__ )) . '/po');
This should make everything work again, and your Mailchimp plugin options in the back end will now also be in the correct language instead of the default english.