Given a fact of failing pure-Tk script, looks like you should ask Tcl people, but asking from both sides (including perlTk) is better

My estimate is 97% probability to fact that the problem lies in underlying C library, which does not recognizes some characters, due to some locale setting on that OS.

I advice for you to ask in those lists: ActiveTcl@listserv.ActiveState.com, tcl-core@lists.sourceforge.net for pure-Tk code, they probably will give you some OS-level advices

OSes I can try on are Linux, Win2000, WinXP, and all they have non-english default locale, which helps with unicode.
Due to my non-native English, as you already could notice...

addition I think failing with only few characters from Unicode means you do not have recent enough version. Can you check somehow which Unicode version your system uses? Also which version of Tcl/Tk do you hav eon those systems?

For tcl version, feed puts $tcl_version to tclsh