Hey Cristobal,
Thank you for reaching out to us!
The days of the week and month names are translated by the WordPress core (The Events Calendar simply uses wp_locale to handle this).
Have you tried to update your WordPress language to Galician? To change your WordPress language, please navigate to Settings > General > Site Language and select from the list of available languages.
Does it help you to solve the problem? If you have any other questions at all please feel free to let me know and I’d be happy to help as best I can!
Cheers,
Patricia