Google Assistant can do a lot of awesome things, but that list would be much shorter without developer support. That's what Actions on Google is all about—it helps developers integrate apps and services with Assistant. Thus, you can shout at your phone and smart speakers more often. Now, developers can start supporting the Chinese (traditional) language in their Actions.
Google services don't work in mainland China, so the only locale currently supported for Chinese is Taiwan (zh-TW). When communicating with a non-native Action via Assistant, you usually need to ask to "talk" to it with a trigger phrase (Assistant itself already speaks Chinese). It's difficult for us people who don't speak Chinese to gauge the usefulness of the triggers, but here they are.
Google also has some examples of how users can access Actions.
Chinese is supported for developers right now, but that doesn't do much for users. Devs can localize existing Actions for Taiwan or build entirely new services, and that'll take time. Although, Google did develop some new tools to aid localization last year that could speed up the process.