The CoC 5th Edition(that is selectable) is multilingual, so it have spanish translation. I just tested it. Sometimes that index is outdated, and I think the official code repository might need some cleanup. But to also answer your question, you need to be a pro user to be able to have Custom Sheets in games, and you would simply go to the Character sheet repository and go to the right folder, and copy the html, css and (translation file if there is one) and on your game's frontpage go to Settings>Game Settings , scroll down the page and fill in the right fields for html, css, translation files and save.
