why japanese generally shorter than other people

This is something which is already changing. But it was kinda true for a long time. Nowadays the japanese children aren't as short as the generations before them. It's changing... The reason for that? Good question - I'm sure there are already people who know why it is like that. Arn't there researchers who are specialized to that kind of topic?

That depends quite alot of factor. I will say it lies in their genes. However the environmental factor and their lifestyle may cause them to be short in height. Also, you are what you eat. Their food always consist of rice so that maybe possible to make them short in height?!