Ok I resolved it. Post here the solution for someone that has my same problem.
Well, the solution is basically a hack to the plugin itself (NOT the qTranslate plugin, just the other ones ONLY). What you do is find within the plugin the load_plugin_textdomain function call.
Code:
load_plugin_textdomain('your_plugin_identifier', false, dirname( plugin_basename(__FILE__) ) . '/languages');
add_action('init', 'init_textdomain');
function init_textdomain() {
load_plugin_textdomain(''your_plugin_identifier', false, dirname( plugin_basename(__FILE__) ) . '/languages');
}
Thanks to this post: http://www.qianqin.de/qtranslate/forum/viewtopic.php?f=3&t=1800