Hello!  Any time you purchase a computer in one country and transfer it to another, you have to transfer the warranty to that country you are now in filling out this form here.  Unfortunately some computer systems are not sold in certain regions and other accommodations need to be made for warranty support which you found out as the XPS 18 is not sold in Spain.  Dell does warranty their repairs for 90 days however, so if your system failed days before the warranty period ended you would have received a 90 day extension.  As for English issues, you were in Spain where they speak Spanish as a primary language.  You would have to contact Dell US or a Dell support line in a country that speaks English for English support as regional support options are for the majority language. 
I bought an XPS18 in BestBuy in Jun 2014. (~ 1200 USD). I bought a brand product because it was supposed to be reliable and have a worldwide warranty because I was moving to Spain in Jan 2015. I moved to Spain in Feb 2015. In March 2015 the laptop quit charging. It would not charge the battery, not would it work plugged in….  So I called the Spanish DELL support (In Spain), well guess what,  1) They did not speak a word of English. Even the voice mail system had no option in English. 2) The support number was a toll paid number of 1.20 euro/min!! what??? 3) and after a 25 min call and three persons, they said they would not repair it since this model did not exist in Europe. (Eventhough it was under warranty for one year). I happened to be travelling to the Netherlands. I call Dell support there, they were helpful. Eric Braams (Dutch Technical support) helped me change the USA warranty to Europe then picked up the laptop and repaired it. Apparently the motherboard and battery was replaced. OK so fast forward Feb 2016. (11 months later) The Laptop fail yet again!!! Same problem…… I call back the Dell in Netherlands, they said the warranty for the repair was only for 3 months!! How is it that you replace a part that is under warranty and the new warranty of the new part is only 3 months…… Ok how much is to repair the laptop: 905 Euros!!!. Hahaha are they crazy!!!!   So in a nutshell, I bought a Dell product because it has good reliability and their worldwide warranty. Lets put it this way, I can but a cheap Taiwanese computer that can last longer for the same price and has no warranty, why the devil would I buy a DELL product again????  
Poor Customer support for XPS18