A. I don’t know much about CJK fonts. I’m just spitballing. I am also half asleep.
B. It depends where the font is displayed. As you probably know, different Japanese, Korean and Chinese characters, which share history and look similar, share one unicode codepoint, see this Wikipedia article. Which specific glyph is shown is decided by some variable that specifies in what language the text is written:
If the text is somewhere in the GUI (the title bar, the panel, some menu), it is probably decided by your default language and locale. This can be changed somewhere in settings. Changing this would also probably change everything to Japanese.
If the text is somewhere on the web, this is decided by the lang parameter of the website. You can’t change this easily.