When using the "Automatically use current user language for installation"
option, the language returned by the "GetUserDefaultLangID()"
function is preferred by the installer.
This function returns the language identifier for the current user as set under Control Panel
--> Clock and Region
--> Change date, time, or number formats
tab --> Format
With that being said, please make sure that the language under the "Format" dropdown is set to Spanish.
Hope this helps.