WHMCS is an all-in-one domain provisioning, client management, billing/invoicing, and client support solution for any business selling online. HEXONET offers  custom WHMCS modules that are regularly updated to add new features and services. HEXONET's WHMCS reseller and High Performance DomainChecker modules are now available in the Chinese language!.

You can view a demo version here. http://try-whmcs.hexonet.net/ (username:demo / password:demo) and select the Chinese language option in top-right of screen.