Translating a component is a pretty common part of integrating it into your overall site. Like other Joomla components, PBBooking is translated using language files.
Copy the language files from:
/components/com_pbbooking/language/en-GB/en-GB.com_pbbooking.ini to /language/xx-XX/xx-XX.com_pbbooking.ini and
administrator/components/com_pbbooking/language/en-GB/en-GB.com_pbbooking.ini to administrator/language/xx-XX/xx-XX.com_pbbooking.ini
The xx-XX needs to be replaced with your country and language strings.
Then just translate the new files accordingly.
You can also use the Joomla Language Manager GUI. There’s a great tutorial available at this site here https://www.ostraining.com/blog/joomla/languge-manager/.