If I run

  use POSIX qw(locale_h strftime);
  setlocale(LC_ALL, "");
  print (strftime("%a, %d %b %Y %H:%M:%S %z", gmtime()), "\n");

under ru_RU.UTF-8, then the result is completely miscoded - the output is not in
any legal encoding.

The "encoding" of the output can be described as a result of applying a
iso-8859-1..utf-8 conversion to a legal UTF-8 encoding of a Cyrillic time
string. In other words, currently (perl-5.8.0-50, glibc-2.2.93-2)

env LC_ALL=ru_RU.UTF-8 /tmp/test.pl | recode utf-8..iso8859-1

produces a utf-8 encoding of a Cyrillic time string.