On the Booking Listing page exist ability to change language (locale) of emails, that will send to visitor during approving or declining of the booking. But how to detect language/locale of webpage, from where visitor submit the booking.
Here is instruction how to do this.
Also you will be need to add to the "Content of booking fields data" form (its at the bottom of Booking > Settings > Fields page) this shortcode:
<strong>Active Language</strong>:<span class="fieldvalue">[active_language]</span>
For showing this field at the Booking Listing page.