@montty, Please be advised that the lingua franca on this forum is English. You might consider updating your question accordingly allowing everyone to read it.
I cannot change the language to Spanish, within my Desktop…
What does Desktop mean? Do you perhaps mean the language of the UI of plugin Admin?
Please also embed code snippets (system.yaml) properly inside triple backticks (```). We cannot see now if there is any formatting issue with the snippet you show.
@montty, Again, please don’t use the blockquote option, but embed code snippets using triple backticks (```)…
The settings in system.yaml:languages are for multilingual Grav and not for Admin.
The language for the UI of Admin should be set in Admin at the config of the User. Click on the username in the upper left corner and then choose the desired language.