The tutorials are in spanish but honestly, there isn't that much to it. Just create an mexican paypal account with kinda accurate info (you can use a random identity generator page) , and once it's done, add the credit card.
Meanwhile either create a Mexican Nintendo account or change the region of one already created to Mexico (which you remove the funds and lock the gold points in the original region). Enter the eshop with it, and try to link the Paypal account in "Account Information". They'll send you a message to the email linked to the account, and from there it should be obvious.
The problem I have with this is that after I got the email, I tried to link it, but Paypal just sayd "There was a problem linking the account". Wasted like an hour doing it, so I just gave up and bought an 10$ eshop card in Seagm.