Change all day text

You could ‘translate’ it

https://icalevents.com/3445-an-accent-for-your-website/
https://wpusersplugin.com/8519/change-displayed-text-plugin-theme/

OR use css to swop out the content of the ‘allday’ class.
https://css-tricks.com/swapping-out-text-five-different-ways/