(Fedora-18; all desktops)

A user needs all
* menu entries, buttons, prompts, messages, application icon labels, etc.
within
* desktops (Gnome, KDE, Xfce, etc.), all LibreOffice applications, vi, etc.
to be English.

But he needs to be able to both
* enter and view
text in both
* English and  simplified Chinese
within
* vi, all LibreOffice applications, internet e-mail (Yahoo mail, gmail, etc.), etc.
where most files/messages will contain a mix of English and simplified Chinese.

How does root and/or the user set up his account so he always has these abilities?  In effect, we want the account to be bi-lingual, with English as the primary language, and simplified Chinese being a secondary language.

Thank-you in advance for your help.
Bill.