Appointments Booking - Settings - Labels (Changing The Front-End Text)
The plugin settings enable changing any label used on the frontend. This include also messages and labels which appears on the calendar.
To change the labels visit the plugin admin menu and choose Options.
On the options chose the Labels tab.
And edit the labels you want to change.
This includes the calendar appointment status.
Calendar months and other navigation terminology, both in short and complete versions
Booking form messages.
Discussion form messages
And related error messages.