Q: Why did I receive an email from Mac in Japanese?

As a scam you mean?  Sure, I've had fake Apple emails from Russia, China, Korea and I seem to recall one from India too.

see http://www.apple.com/legal/more-resources/phishing/

and Identifying legitimate emails from the iTunes Store - Apple Support

and Identifying fraudulent "phishing" email - Apple Support

Are you talking about junk email? I got some in Cyrillic, Chinese, Arabic... you name it, I got them in my mailbox.