In non-Windows environments, the gpg command is prepended with “LANG=C
LC_ALL=C” to ensure gpg's output is consistent to allow for parsing the
information. However, that doesn't work in Windows and won't
necessarily work if we ever remove the code forcing use of /bin/sh.
Since Vim already knows how to influence the environment, use its
“:language message …” command to set/restore the locale before/after
running the gpg command.
Closesjamessan/vim-gnupg#45
Signed-off-by: James McCoy <vega.james@gmail.com>