Translation / i18n of the mailchimp plugin does not work for me on Wordpress 3.0+. The cause of this seems to be the mailchimpSF_plugin_init function using ≤code>load_plugin_textdomain in the old and deprecated way (mailchimp.php, line 62):

load_plugin_textdomain( 'mailchimp_i18n', MCSF_DIR.'po/');

simply open mailchimp.php and change line 62 to:

load_plugin_textdomain( 'mailchimp_i18n', false, dirname(plugin_basename( __FILE__ )) . '/po');

and translation should work again.