You don't need a Chinese version to write Chinese in OpenOffice. If you want the choice of having the GUI in Chinese or English you will need to have English and Chinese Language packs installed. To write in Chinese you need a Chinese input method and have the correct settings under Tools>Options...>Language Settings. In particular you will want to have Enhanced Language Support enabled for Asian languages.
For a Chinese version go to:http://zh.openoffice.org/new/index.html
But if you already have an English version installed you will just want to install the Chinese language pack.