During period, Europe had only limited contact and trade with Asia and there are, relatively, few people with Asian personae in the SCA. Although just because there was less contact with Asia in period, does not mean this should discourage you from exlporing asian personas!
Some people may have issues with Japanese personas, because there are only twelve documented people from Japan in period. You could also argue that there should not be a problem with Japanese personas because there is documentation of the Japanese being in Europe at that time. It may be minimal documentation, but it is documentation nonetheless!