Greasy Fork is available in English.
Fixes Han unification, for example, for Japanese (can be edited to prioritize other langs)
当前为
It is exactly similar to http://greasyfork.icu/en/scripts/439780-wanikani-community-prioritize-japanese-glyphs but add more websites.
This script may also be edited to prioritize other langs, like "zh-TW" or "ko-KR", if you really need it.
It is possible to edit the UserScript to add more websites, as well as use regular expression, if @match isn't sufficient.
The script is based on lang attribute, and no CSS is really being injected. (I might add CSS injection, based on common fonts, later.)
This partially related to an Arch Linux issue on Firefox., which is fixed as a separated script.