Users can not log-in using the password sent to their email. The registration process is OK, however, using the password generated by Wordpress will not log them in. This applies on either copy the password from the browser just after activating a user, or copying it from the password email (or manually writing it). When Pro Site is deactivated or Signup on Checkout is unchecked passwords works.
I'm on a fresh Arabic Wordpress installation with no other plug-in activated, and using Twenty Fifteen theme.