When you first launch Windows 8 or 8.1 it should give you an option to choose your language. If you're going to be using the pre-installed OS, you just choose a language, make some personalizations such as setting theme and background colors. Similar to that is installing a fresh copy of Windows 8 or 8.1.
Follow this guide if you're going to be installing a fresh copy of Windows 8 or 8.1.
If you don't want to go through the hassle of installing a fresh copy and there is no option to change languages, then simply install the chinese version by following a video or guide and install the language pack from inside Windows. Here is a quick video on how to add languages.