Does a supervisor have to read a thesis of his PhD student
Have to is a strong requirement. In the US, the supervisor is almost always part of the examining committee so at some point they will have to read it. Some departments may have rules about feedback on drafts and how quickly and how much feedback supervisors can provide.

In the UK, the supervisor is almost never part of the examining committee. While I have never seen regulations prohibiting feedback, but there is more of a culture that students should stand on their own. That said, I think most supervisorsuccessful read a draft of a thesis.