To answer your questions from PM, depending on the examiner it can be good or bad. Weather questions are likely to be asked because Japan has a wide variety of weather pattern. Many questions will be from AIM-J. I think they won't ask much questions from A320 because you probably already know, so they focus more on AIM and 'how to fly in Japan' stuff. I know one examiner love to ask about aerodynamics, and some stuff that you probably already forgot from the old school days. It's always good to know the limitations and critical stuff that may relate to actual flying. I believe company have a question bank from oral exam. All airlines in Japan shares each examiners and inspectors oral question on every fleet.
SIM failure rate... now these days I don't hear many failure for the practical exam. Profile is straight forward. It's a 'show time'. Your SIM instructor knows how to pass the SIM check so just do what he says and you'll be fine. Japan is still Galapagos in aviation in many aspects, so you have to demonstrate VFR traffic patterns, minimum circle to land from instrument approach, and so on. At many airports, we still do visual approaches or minimum circle in IMC. I hear more failure in oral exam than practical.
Regarding Japanese Radio License, now these days I'm not too sure. I'm currently asking one of the staff regarding this. I'll post it here once I have an answer.
Good day and stay healthy!