After Linux Mint is installed in English, the default language of the Firefox browser is English. You can use the official plug-in to change to Chinese.
http://ftp.mozilla.org/pub/firefox/releases/60.0.2/linux-x86_64/xpi/zh-CN.xpiAmong them, the number in the middle is the version number of the browser, which can be viewed in help-about firefox.
After the number is the system format, fill in linux-x86_64 for a 64-bit system, and fill in linux-i686 for a 32-bit system.