Wow don't need to be on an install path to work, you can install it on your c:\ and copy it on your z:\ removable harddrive it will still work the same. So duplicating your client and patching it separatly won't be a problem(I did it recently), but! as long as one of the version can be on an unplugged harddrive.
When lauching the patch you can't choose the game folder, so if you have 2 who can be patched it can be a little messy. I had some troubles patching a chinese client with a chinese patch caus it would try to patch my english client... weird I know.
And as far as ping is concerned, I'm not from US so I can't comfirm, it seems it's ok for solo(below 500ms) but if your client start to brew other players info it can be a little laggy.
When you log on a realm type "/join english
" to get in touch with the community members.
WoW English/Chinese glossary
(2000+ translated words) found on wow-in-chinese.jfs-web.chEnglish speakers are consolidating on the same realm for Cataclysm check this thread