No, as far as I know, HTML elements can only have one language specified. The community page is set to US English using
<html lang="en-US" ...>. The WK team could probably change a setting in Discourse to let it be
<html lang="ja-JP" ...>, but that would be wrong since ~99% of the forum is in English. So the settings in your screenshot won’t have any influence as long as your webbrowser doesn’t identify the language as being Japanese.
When your webbrowser has to display a kanji, it has to guess what language it is. If the text is within an HTML element that has
lang="ja-JP" specified, this is easy. Otherwise, it has to look for other hints – maybe the system language, maybe the languages you have specified as your preferred languages within the webbrowser, etc.
Screenshots of browser settings
I’m on Windows, and Chromium-based Edge displays 直 (the Chinese version) until I add Japanese as a preferred language:
My Firefox already guessed by default that it’s Japanese (maybe because I have an IME installed?), but I still experimented with the language settings:
When I added Chinese, Firefox switched to the Chinese kanji.
Of course, you also need a Japanese font installed on your system, otherwise the webbrowser still has to fall back to a Chinese font.
Ideally, everyone posting text in a different language than the page’s default US English would enclose it in an HTML element with the correct language specified:
<span lang="ja-JP">直</span>, but that’s pretty cumbersome. That’s why I let my IME2Furigana userscript add
lang="ja-JP" automatically to every ruby-element. #ad