Check out the code for the IntenseDebate comments system and make sure where the Comments variable is initiated it looks like this
__("Comments", "your-theme"),
A double under-score denotes it to be translated. “Comments” is the interface element and “your-theme” is the theme translation initiator that should be in you functions.php theme file
// Make theme available for translation
// Translations can be filed in the /languages/ directory
load_theme_textdomain( 'your-theme', TEMPLATEPATH . '/languages' );