Thank you, it worked emptying the field “To (Email Address)” into Booking Package > General Setting!
About “Room” question, I started my italian translation from the .pot included in wp-content/plugins/booking-package/languages and Poedit (v. 1.8.1) couldn’t find any occurrence of ‘Room’…
But now, it doesn’t matter as I added it manually.
Best regards,
Simone