Return Value of load_plugin_textdomain

by 

global $langOK;
add_action( 'plugins_loaded', 'myplugin_load_textdomain' );
function myplugin_load_textdomain() {
    global $langOK;
    $langOK = load_plugin_textdomain( 'my-plugin', false, dirname( plugin_basename( __FILE__ ) ) . '/languages' );
}

Later you can check the value of $langOK ( TRUE = success, FALSE = failure ).