WordPress plugin that alters the (translated) title attribute for `wp_list_categories()` list items on the fly using the `gettext` or `category_description` filter.

wcm_list_cat_filter.class.php

<?php
add_action( 'plugins_loaded', array( 'WCM_list_cat_filter', 'init' ), 5 );
/**
 * @package    WCM Filterama
 * @subpackage Bootstrap
 */
class WCM_list_cat_filter
{
	private static $instance;

	public $args;

	static function init()
	{
		null === self :: $instance AND self :: $instance = new self;
		return self :: $instance;
	}

	public function __construct()
	{
		add_filter( 'get_categories_taxonomy', array( $this, 'get_args' ), 10, 2 );
	}

	/**
	 * Attached from inside get_categories()
	 * @param  string $taxonomy
	 * @param  array $args
	 * @return string
	 */
	public function get_args( $taxonomy, $args )
	{
		$this->args = $args;
		add_filter( 'list_cats', array( $this, 'route_filters' ), 10, 2 );
		return $taxonomy;
	}

	/**
	 * Attached from inside walk_category_tree()
	 * Intercepted inside Walker_Category::start_el()
	 */
	public function route_filters( $cat_name, $cat )
	{
		if (
			0 === $this->args['use_desc_for_title']
			OR empty( $cat_name )
			)
		{
			add_filter( 'gettext', array( $this, 'alter_title_attr' ), 10, 2 );
		}
		else
		{
			add_filter( 'category_description', array( $this, 'alter_cat_attr' ), 10, 2 );
		}

		return $cat_name;
	}

	public function alter_title_attr( $text, $domain )
	{
		remove_filter( current_filter(), array( $this, __FUNCTION__ ) );
		return $text = 'YOUR STRING HERE';
	}

	public function alter_cat_attr( $cat_desc, $cat )
	{
		return $cat_desc = 'YOUR STRING HERE';
	}
}