Adding another arg to comments_popup_link

Filter 'comments_number'. You get the translated number and the real number as arguments. Return what fits best.

Sample code:

add_filter( 'comments_number', 'wpse_31328_comments_number_i18n', 10, 2 );

function wpse_31328_comments_number_i18n( $text, $number )
{
    if ( 2 === $number )
    {
        return _x( '2 comments', 'comments number', 'your_text_domain' );
        // or hard coded:
        // return '2 komentarja';
    }

    return $text
}