If you edit the booking form, you will see a lot of options are added using custom fields and they don't have any translations preferences, as a result they aren't added to form translations, one of which is availability, I suggest you to visit the booking form hidden link and mark all custom fields as copy, then update the form to see if it works.
You can also ask the plugin author which custom fields needs to be copied in translations to make it work properly.
I see that there is no terms and conditions on the french booking page, can you please let me know how you can enable the terms and conditions check while creating the form?
There must be some feature within the plugin that enables this options, I tried to search for it but couldn't find it, being so, can you reach out the plugin author and ask how the terms and conditions page can be enabled and since the plugin author mentions WPML compatibility, ask them if they can check this quickly and suggest a better workflow.
