Reference:
http://mail.gnome.org/archives/gnome-i18n/2002-January/msg00169.html
(the third bug mentioned by Christian)

Suppose you are running gedit and you want to do the "Copy" operation
using the keyboard and the Ctrl+C shortcut.
For the POSIX locale, you would press "Ctrl+C" to to Copy the selected 
text in the "clipboard".
It is possible to change the shortcut with an other one, 
one where the shortcut letter is a localised letter.
For Ctrl-C, you would click to open the Edit menu, then with the
keyboard
and the arrow keys you would go down to "Copy" and at that point you
would press "Ctrl-x", where "x" is the appropriate letter (Greek in my
case).

However, there is a bug here. Instead, the latin letter appears as the
new
shortcut instead of the Greek letter. As if the non-latin letter is
ignored.

To show that this is a problem, the bug exists for Ctrl-x shortcuts
only.
Alt-x shortcuts where x is a Greek (non-latin) letter work perfectly.

As a sidenote, when someone is in the above point to choose the new 
shortcut and tries to press "Alt-Shift" (which normally changes the XKB
keyboard between different languages), the "Alt-ISO_Prev_Group"
character
is grabbed instead of being ignored.