Translation of custom field messages

Hi,
I have a problem with the translation of the messages of the custom fields created.
First I create a field called “He leído y acepto la Política de Privacidad” in the backend.
Second, I go to the reservation record on the frontend, I connect from the plugin and it shows me the message “He leído y acepto la Política de Privacidad can’t be empty”.
That piece of code “can’t be empty” should be able to translate and I can’t find the translate function.
Could you tell me where is the path of the translation function for the line “He leído y acepto la Política de Privacidad can’t be empty” or the line “can’t be empty”?

I leave a screenshot of how the message is displayed:
https://ibb.co/3Sw6tLM

Thanks and best regards.