Language bug

The language file is not loaded.
After review your code, I found that you place the load_plugin_textdomain in the constructor, see the follow:

/**
* Constructor
*/
function ReOrderPostWithinCategory() {
   load_plugin_textdomain('deefusereorder', false, basename(dirname(__FILE__)) . '/languages');

The load_plugin_textdomain function should be called only in the WordPress init hook.

Quick resovle:

I place the load_plugin_textdomain in the saveOptionPlugin function.

//Action qui sauvegardera le paamétrage du plugin
add_action('init', array(&$this, 'saveOptionPlugin'));

It Works.