Bug#249951: xlibs: Ctrl key not seen correctly when Russian layout used
This issue is discussed in
The Ctrl key works as expected if 'us,ru' layout is selected ('us' can
be replaced by any Latin-based layout). The problem is that Russian
users surely prefer 'ru,us'. A patch discussed in the thread above
fixes this problem by looking for ASCII characters in all groups
(and not only in the first one as of now), it has been incorporated
into CVS 3.18 (2003-04-19) of
Maybe you can ask Debian XFree86 maintainers to backport this patch
if you believe that it is important.
But note that the Ctrl key won't work with 'ru' layout.