After updating plasma and kde to 5.14.3/5.52.0, Chinese localization is missing for almost all interface in KDE
Is "CH" in the summary just a typo or have you actually tried to use it? "CH" country tag is for Confoederatio Helvetica (also called Switzerland), not China. For China, you would want "CN" country tag, so "zh_CN" as full locale name.
There's not much we can do without any information about your LINGUAS settings.
Its a typo, of course it is zh_CN locale output: locale LANG=zh_CN.UTF-8 LC_CTYPE="zh_CN.UTF-8" LC_NUMERIC="zh_CN.UTF-8" LC_TIME="zh_CN.UTF-8" LC_COLLATE="zh_CN.UTF-8" LC_MONETARY="zh_CN.UTF-8" LC_MESSAGES="zh_CN.UTF-8" LC_PAPER="zh_CN.UTF-8" LC_NAME="zh_CN.UTF-8" LC_ADDRESS="zh_CN.UTF-8" LC_TELEPHONE="zh_CN.UTF-8" LC_MEASUREMENT="zh_CN.UTF-8" LC_IDENTIFICATION="zh_CN.UTF-8"
sorry forgot to include LINGUAS="ru zh-CN"
LINGUAS usage has always been zh_CN, *not* zh-CN.