To begin with, generate a contract or an invoice. If you need help with that, these FAQs will instruct you: Generate invoices for your bookings, How to create a booking contract.
At the upper right corner, you will find the possibility to change the language of the preset fields like place, date or signature.
Notice that the language of the tool itself will not change, only the values visible in the contract or invoice will appear in the selected language, for example the date and the signature field:
