This is actually a tk and tkinter issue rather than IDLE issue as such.  Python code can only catch Python exceptions, and I believe that the Xserver crash does not result in one.  These crashes were reported on a different issue and the conclusion there is that there is nothing we know to do.

IDLE uses the default tkFixedFont unless the user selects another one.  If tk selects a font that crashes, that is not IDLE's fault, or even tkinter's.  If there were a font that was always available on every *nix system and that never crashed for any unicode char, then IDLE could select that on *nix systems.  But I have no idea of such.  (Courier serves that purpose on Windows, and it is the tkFixedFont font on Windows.)

In the meanwhile, users can select a different font upon startup, which only uses ascii chars (if one starts with Shell and no editor).  Select Options => Configure IDLE.  Possible use the font sample box to try out the problematic chars but pasting or otherwise inserting.  If IDLE crashes, try again.  The resolution of this issue might be to say something more in the doc about this problem, as people seem to be using non-ascii more often, or maybe more ofter loading fonts that do not work.

Serhiy, can you say any more?  You know much more about tk/tkinter default font choices and Xserver font crashes than I do.