Japan did not sign the 1968 Vienna Convention on Road Traffic, effective 1977, just like China, USA, and many others. Other than Korea they make exceptions.

Japan acccepts Carnet de Passage but claims authentification of German CdP by Japan Automobile Federation. Import of German plated vehicles requires inspection and registration in Japan for temporary import, similar to China.

We are not sure yet if 20 year old trucks will have to meet current emission standards…