Adding language packs to an existing Siebel installation

I am hoping somebody can help me out here.  I need to install some additional language packs to an existing Siebel implementation and am a bit confused.  We have a v8.1.1.9 implementation on a Windows server using an Oracle 11g database.  When the server was originally built, we installed v8.1.1.0 and  then patched it to v8.1.1.9.  My understanding is that I need to uninstall the 8.1.1.9, then I should be able to add the language packs, then patch back to the 8.1.1.9 level.  My questions are:

How do I uninstall the 8.1.1.9 now?  In prior versions, I would go to Add/Remove programs in the control panel and start the Siebel installer and choose maintenance uninstall.  In this release everything has changed and I am seeing conflicting procedures.  Some say to use the rolback.bat, others say to uninstall everything....what is the correct procedure to remove 8.1.1.9 and revert back to the 87.1.1.0?