Answer to b: Dialect

Even in Japan, I can find cultural differences from place to place. Especially, the differences of dialect is very interesting and surprising subject. In Japan, there are many unique dialect, and people sometime can't understand what they said.
In my case, I recognized the differences when I was 9 years ago. About 10 years ago, I moved from Yokohama to Amagasaki. At that time, I was very surprised that all of the people I talked to spoke strange words. It was very hard for me to get accustomed to it, but I can't still use Kansai dialect very well.
I think these are come from the diversity of local cultures. In Japan, cultures have their own characteristics by region from ancient time, so sometime they have different viewpoint about one thing. In such a situation, It is not so strange that there are many dialects.