What is "standard English"?

1. Is there a standard English? If so, what is it? If not, why not?

2. Is there a standard US English? Is there a standard British English? Why or why not?

3. Is there a standard Australian, NZ, Canadian English? What about a standard Singaporean or Indian English?

4. Could academic English or test English be standard? Why or why not?

5. Do you think there could ever be a "standard" Japanese English?