Change default font to MotoyaLCedar for Japanese

The default font was not correctly configured for a long time for Japanese. As a result, Japanese font typeface (glyph) was not rendered correctly since Debian 9 (stretch) because of Han Unification issue.

So, the default font must be changed to render Japanese typeface (glyph).

MotoyaLCedar is compact enough compared to other candidate Japanese fonts with considering pros. and cons. (font size, the readability and visibility improvements), MotoyaLCedar is the best in practical use-case.

See https://people.debian.org/~kenhys/bug-1037256/

(Ideally it might be BIZ UDGothic is best because it is universal design font and it gives neat and clear impression, the best readability and visibility, but it takes huge amount of extra disk usage.)