I noticed that STALKER-SoC has been updated recently, in the changelog: Added support for Traditional Chinese Localization (text only).

It means that Traditional Chinese interface support has been added? but how to enable it? The offline installer doesn't have this option, and I didn't see anything to setup after installation.

If you're okay with using Galaxy, you'd install STALKER as usual, then go to the "Manage Installation" menu, and select "Configure". That'll give you the option to switch to whichever language you want, and Chinese does appear to be on that list.

With the standalone installers, I'm not sure.

For offline installer you need to download correct version. See picture.

Thanks for the answer