>You are missing the point on using Tcl_CreateObjCommand, I didn't mean
>to just go and and do s/Tcl_CreateCommand/Tcl_CreateObjCommand/ because
>if you are going to convert everything to unicode then there is no
>point in using Tcl_CreateObjCommand.

I'm not tcl/tk expert, so probably missng many things. :-(
Can you explain how to solve this issue by moving to Tcl_CreateObjCommand?

>Also, Tcl_ObjCmdProc should use Tcl_Obj *CONST objv[] instead of
>Tcl_Obj *const objv[] because Tcl may define CONST as nothing, and it
>uses CONST when defining Tcl_ObjCmdProc.

I created adhok.patch just for explanation. This is not solution. I used
Tcl_CreateObjCommand + Tcl_GetUnicode to demonstrate Tcl converts
'\xc0\x80' to null byte. (adhok.patch contained Japanese characters, so
I'll repost that as just_for_explanation.patch)