CJK Shared Ideographs have different variants in terms of their shapes and sometimes structures. Take a look at the screenshot below, which is from one of my entries at lang-8.com. It's based on the language being used that a variant is selected to render the contents.
I wrote this script to fix the problem at lang-8 of display of Japanese Characters with the Chinese-specific glyphs. I guess it would work for other languages as well, but I have not tested it. It automatically detects the language used and adds "lang" tag to various HTML tags on journal pages on lang-8.com, to hint the brower so as to enable display of language-specific glyphs of CJK ideographs.
Note that you need to use an OpenType font that supports "localized forms" to make it work (in case you don't, the script can also work well, but the fonts displayed is inconsistent). I am using Adobe Source Han Sans. Also slight adjustments to the css configuration are needed to force the browser to use your font. You may want to use my userstyle to take a look: (https://userstyles.org/styles/138564/lang-8-com-fix-cjk-ideographs-display)
This script utilizes guessLanguage.js library authored by Rich Tibbett licensed under LGPL. This script itself is licensed under GPL.