Some strings present in the .po files do not exist in the .mo files
installed by grub-common. For example, if you run "grub-mkconfig --help"
under a zh_CN locale, you'll find that the translation is incomplete, but
translation of "output generated config to FILE [default=stdout]" exists
in zh_CN.po in the source code. The problem is this string doesn't exist
in /usr/share/locale/zh_CN/LC_MESSAGES/grub.mo. This also applies to other
languages like French, and other strings like the "Loading Linux %s ..."
boot message.

Hi,

I took some time looking into this bug. It seems that strings from
files listed in po/POTFILES-shell.in are not included in the generated
grub.pot file. Relevant commands in the build log are:

case `/usr/bin/xgettext --version | sed 1q | sed -e 's,^[^0-9]*,,'` in \
  '' | 0.[0-9] | 0.[0-9].* | 0.1[0-5] | 0.1[0-5].* | 0.16 | 0.16.[0-1]*) \
    /usr/bin/xgettext --default-domain=grub --directory=../../.. \
      --add-comments=TRANSLATORS: --keyword=_ --keyword=N_
--flag=_:1:pass-c-format --flag=N_:1:pass-c-format
--flag=error:3:c-format --flag=error_at_line:5:c-format
--from-code=UTF-8 ${end_of_xgettext_options+}
--flag=argp_error:2:c-format --flag=argp_failure:4:c-format
--flag=error:3:c-format --flag=error_at_line:5:c-format \
      --files-from=../../../po/POTFILES.in \
      --copyright-holder='Free Software Foundation, Inc.' \
      --msgid-bugs-address="$msgid_bugs_address" \
    ;; \
  *) \
    /usr/bin/xgettext --default-domain=grub --directory=../../.. \
      --add-comments=TRANSLATORS: --keyword=_ --keyword=N_
--flag=_:1:pass-c-format --flag=N_:1:pass-c-format
--flag=error:3:c-format --flag=error_at_line:5:c-format
--from-code=UTF-8 ${end_of_xgettext_options+}
--flag=argp_error:2:c-format --flag=argp_failure:4:c-format
--flag=error:3:c-format --flag=error_at_line:5:c-format \
      --files-from=../../../po/POTFILES.in \
      --copyright-holder='Free Software Foundation, Inc.' \
      --package-name="${package_gnu}grub" \
      --package-version='2.06' \
      --msgid-bugs-address="$msgid_bugs_address" \
    ;; \
esac

There should be some other xgettext invocations to include strings in
POTFILES-shell.in, using the option
--files-from=../../../po/POTFILES-shell.in. See the corresponding
commands in po/Makefile.in.in in the source code tree. After building
the package, the commands to include strings in POTFILES-shell.in are
present in the backup file Makefile.in.in~, but not in the regenerated
Makefile.in.in.

Note that po/gettext-patches/0001-Support-POTFILES-shell.patch will
fix the Makefile. So it's likely that these gettext patches are
erroneously not applied.