Hi,
Recently (my gut feeling says since the last updates in March/April 2014), I have similar issues, i.e. not being able to use Google Pinyin as my main Chinese input engine. The issue holds true for ALL Office 2013 programmes. However, Chinese input (Google
Pinyin 2.7.24.126) works very well on any other applications such as Firefox (你看看), NotePad++, Skype, MindManager, et al.
I followed the instructions on how to add new language using the control panel language applet, read and tried the instructions on your mentioned article on "Type or edit text in a different language", uninstalled Google Pinyin, uninstalled the Chinese language
pack, restarted my Windows 8.1 laptop, reinstalled the language pack and Google Pinyin, temporarily changed the default input language into Chinese, and various other tips I found that I haven't listed here. Result: Chinese input STILL NOT WORKING.
Problem is: I'm running out of ideas and need my Chinese input while I need to communicate with my colleagues, vendors, and customers who are not able to communicate other than Chinese! Using workarounds is only a temporary fix. But I am looking for a permanent
one, which I seem not to find. (And I see reinstalling my laptop only as a last resort option that I would like to avoid at any cost - which also doesn't guarantee success.)