We should add the sample notices for bookings placed,cancellation, and modification via a DB rev for existing installs. As of now the library has to create them with no reference
There is refernce - if they create a notice with the language code, they can use the reset feature to pull the translated text.
There is no switch to turn them off. Koha will start sending them as soon as they are created, that's why I was against adding them out of the box (keep the behavior consistent). Especially since we only add them by default in English.