Update es_es.php

With some time i will help you checking the whole translation, i just need those lines by now. What can we do if i translate the menu and other strings? They're part of core files and don't have string variables like this, i suggest do that in order to make the translations more clean and of course, more affordable.

Greetings ~
Merge pull request #25 from ignizh/patch-1

Update es_es.php