I checked, it needs one of these :)

lib/open.t
 225 $ENV{LC_ALL} = $ENV{LANG} = 'ru_RU.KOI8-R';

t/op/exec.t
  33 $ENV{LC_ALL}   = 'C';           # Forge English error messages.


t/op/groups.t
  10     $ENV{LC_ALL} = "C"; # so that external utilities speak Englis
+h


t/op/lfs.t
 119 $ENV{LC_ALL} = "C";
[download]

Though on my win32/mingw machine ls.exe doesn't seem to respond to LC_ALL or LANG at all, so I can't exactly test this :)