论点topic_count_text_callback 无法执行您需要的操作，因为它没有将术语ID和分类法作为参数。这应该固定在核心 我想我以后会为此写一个补丁

更新：我已经为Ticket #21198. 里程碑是3.6，因此以下答案最终将过时。我会更新这个帖子

但并非所有的希望都破灭了。我们可以在上筛选生成的标记wp_tag_cloud, 对其运行regex并从class 属性和第二个参数的分类$args. 然后，我们使用术语ID和分类法来获取术语描述并替换原始标题属性。

add_filter(
    \'wp_tag_cloud\', # filter name
    array ( \'WPSE_78426_Tag_Cloud_Filter\', \'filter_cloud\' ), # callback
    10, # priority
    2   # number of arguments
);

/**
 * Replace title attribut in a tag cloud with term description
 *
 * @author toscho http://toscho.de
 */
class WPSE_78426_Tag_Cloud_Filter
{
    /**
     * Current taxonomy
     *
     * @type string
     */
    protected static $taxonomy = \'post_tag\';

    /**
     * Register current taxonomy and catch term id per regex.
     *
     * @wp-hook wp_tag_cloud
     * @uses    preg_callback()
     * @param   string $tagcloud Tab cloud markup
     * @param   array  $args Original arguments for wp_tag_cloud() call
     * @return  string Changed markup
     */
    public static function filter_cloud( $tagcloud, $args )
    {
        // store the taxonomy for later use in our callback
        self::$taxonomy = $args[\'taxonomy\'];

        return preg_replace_callback(
            \'~class=\\\'tag-link-(\\d+)\\\' title=\\\'([^\\\']+)\\\'~m\',
            array ( __CLASS__, \'preg_callback\' ),
            $tagcloud
        );
    }

    /**
     * Replace content of title attribute.
     *
     * @param array $matches
     *        $matches[0] = complete matched string,
     *        $matches[1] = term id,
     *        $matches[2] = original content of title attribute
     * @return string
     */
    protected static function preg_callback( $matches )
    {
        $term_id = $matches[1];
        // get term description
        $desc = term_description( $term_id, self::$taxonomy );
        // remove HTML
        $desc = wp_strip_all_tags( $desc, TRUE );
        // escape unsafe chacters
        $desc = esc_attr( $desc );

        // rebuild the attributes, keep delimiters (\') intact
        // for other filters
        return "class=\'tag-link-$term_id\' title=\'$desc\'";
    }
}

结果