一种可能的方法是：在函数中添加过滤器。主题的php：

add_filter ( \'wp_tag_cloud\', \'tag_cloud_slug_class\' );

function tag_cloud_slug_class( $taglinks ) {
    $tags = explode(\'</a>\', $taglinks);
    $regex = "#(.*tag-link[-])(.*)(\' title.*)#e";
        foreach( $tags as $tag ) {
        $tagn[] = preg_replace($regex, "(\'$1$2 tag-\'.get_tag($2)->slug.\'$3\')", $tag );
        }
    $taglinks = implode(\'</a>\', $tagn);
    return $taglinks;
}