added i18n support on validation and Spanish error messages

Maybe you'd like to add this to the project. I know there are a lot of ways to manage Internationalization.
With the code I added to manage i18n you can call a function t("KEY") or t("message") I choosed the first one as is more generic, but the second one is easier for coding.  if you'd like any modifications just let me know.

PS: Still need to create tests but I do not want to interfere with yours, any recomendation ? new test for each case ?