Yes. You can accept orders from buyers based anywhere in the world.
Please note that the language of the payment page depends on the end user's browser settings. If a user is based in Japan and their computer settings are in Japanese, they will see the Japanese version of the purchase page. If the user is based outside of Japan, they will see the English version.
However, if the user is logged into their SPIKE account, the language settings they have chosen in their user dashboard will take precedence.
*SPIKE is currently only available in Japanese and English.