This process of adding Chinese is a bit more complicated than for other languages.
In MX Package Installer, open the category “Languages” and install Chinese ibus as well as the font packages.
Some users believe that fcitx is to be preferred now over ibus due to recent changes.
Also install the language packs for Firefox, Thunderbird and LibreOffice if you use them.
Run im-config -n ibus (or: im-config -n fcitx) and configure. if im-config is not present, install it from the repos. (Note that this universal command may not work in antiX, and the specific ibus-setup or fcitx-setup should be used instead.)
If this is being added to other languages already present, click All settings > Keyboard > Layout tab: uncheck “Use system defaults,” click the Add button and select Chinese.