The Search Engine to Chinese language
The default search plugin, nodebb-plugin-dbsearch, is using the database built-in full text search functionality, which is usually fairly limited, but since it's included with the database doesn't require additional configuration from the user and can just work "out of the box".
MongoDB for example only supports 15 languages, all of which use the latin alphabet (with some accented letters but that's it): https://www.mongodb.com/docs/manual/reference/text-search-languages/
Postgres similarly doesn't support Chinese, but apparently there is some extension (but I'm not sure if the dbsearch would work with it). Redis now has some native support but it seems to require additional setup so I'm also not sure if the dbsearch plugin works with that.
A backend that seems to work significantly better is Meilisearch which I maintain support for via nodebb-plugin-meilisearch.
Aside from supporting more languages, it adds a few nice features like prefix search, typo tolerance, synonyms or ignoring stop words. But, as mentioned, this is a separate backend, so it requires running an additional service somewhere (same server as NodeBB is the easiest to do since then everything is local, so no need to worry about network latency or security, but you can also host it on a separate machine if necessary)