I'm building a grub2 memdisk image.

Exec of

    grub2-mkstandalone \
     --compress=no \
     --locales="en@quot" \
     --fonts="unicode" \
     --themes="" \
     -O x86_64-xen \
     -o grub-x86_64-xen \
     boot/grub/grub.cfg

fails

    grub2-mkstandalone: error: cannot find locale `en@quot'.

This is because the required grub2.mo for en@quote is missing

    tree /usr/share/locale/en@quot/
        /usr/share/locale/en@quot/
        ��������� LC_MESSAGES
    find /usr/share/locale -type f -name grub2.mo | grep -i en
        (empty)

Only

    find /usr/share/locale* -type f -name grub2.mo
        /usr/share/locale/pa/LC_MESSAGES/grub2.mo
        /usr/share/locale/ca/LC_MESSAGES/grub2.mo
        /usr/share/locale/zh_CN/LC_MESSAGES/grub2.mo
        /usr/share/locale/de/LC_MESSAGES/grub2.mo
        /usr/share/locale/vi/LC_MESSAGES/grub2.mo
        /usr/share/locale/tr/LC_MESSAGES/grub2.mo
        /usr/share/locale/id/LC_MESSAGES/grub2.mo
        /usr/share/locale/nl/LC_MESSAGES/grub2.mo
        /usr/share/locale/lt/LC_MESSAGES/grub2.mo
        /usr/share/locale/sl/LC_MESSAGES/grub2.mo
        /usr/share/locale/da/LC_MESSAGES/grub2.mo
        /usr/share/locale/ast/LC_MESSAGES/grub2.mo
        /usr/share/locale/fr/LC_MESSAGES/grub2.mo
        /usr/share/locale/hu/LC_MESSAGES/grub2.mo
        /usr/share/locale/ja/LC_MESSAGES/grub2.mo
        /usr/share/locale/uk/LC_MESSAGES/grub2.mo
        /usr/share/locale/fi/LC_MESSAGES/grub2.mo
        /usr/share/locale/es/LC_MESSAGES/grub2.mo
        /usr/share/locale/ru/LC_MESSAGES/grub2.mo
        /usr/share/locale/sv/LC_MESSAGES/grub2.mo
        /usr/share/locale/gl/LC_MESSAGES/grub2.mo
        /usr/share/locale/it/LC_MESSAGES/grub2.mo
        /usr/share/locale/pl/LC_MESSAGES/grub2.mo
        /usr/share/locale/nb/LC_MESSAGES/grub2.mo
        /usr/share/locale/eo/LC_MESSAGES/grub2.mo
        /usr/share/locale/zh_TW/LC_MESSAGES/grub2.mo
        /usr/share/locale/pt_BR/LC_MESSAGES/grub2.mo

are available, where

    rpm -q --whatprovides /usr/share/locale/*/LC_MESSAGES/grub2.mo | uniq
        grub2-2.02~beta2-20.10.1.x86_64

Testing with upstream source

    git clone git://git.savannah.gnu.org/grub.git
    cd grub
    git reflog
        1 2066766 HEAD@{0}: clone: from git://git.savannah.gnu.org/grub.git
    ./linguas.sh
    ./autogen.sh
    ./configure --prefix=/usr/local/grub2-test
        ...
        config.status: executing po-directories commands
        config.status: creating po/POTFILES
        config.status: creating po/Makefile
        *******************************************************
        GRUB2 will be compiled with following components:
        Platform: i386-pc
        With devmapper support: No (need libdevmapper header)
        With memory debugging: No
        With disk cache statistics: No
        With boot time statistics: No
        efiemu runtime: Yes
        grub-mkfont: Yes
        grub-mount: No (need FUSE library)
        starfield theme: Yes
        With DejaVuSans font from /usr/share/fonts/truetype/DejaVuSans.ttf
        With libzfs support: No (need zfs library)
        Build-time grub-mkfont: Yes
        With unifont from /usr/share/fonts/uni/unifont.pcf.gz
        With liblzma from -llzma (support for XZ-compressed mips images)
        *******************************************************

The .mo files are built/installed

    cd po
    make
    make install
    find /usr/local/grub2-test/ -type f -name '*grub*' | grep "en"
        /usr/local/grub2-test/share/locale/en@piglatin/LC_MESSAGES/grub.mo
        /usr/local/grub2-test/share/locale/en@greek/LC_MESSAGES/grub.mo
        /usr/local/grub2-test/share/locale/en@hebrew/LC_MESSAGES/grub.mo
        /usr/local/grub2-test/share/locale/en@quot/LC_MESSAGES/grub.mo
        /usr/local/grub2-test/share/locale/en@arabic/LC_MESSAGES/grub.mo
        /usr/local/grub2-test/share/locale/en@cyrillic/LC_MESSAGES/grub.mo

No idea where the *rest* of the locales, e.g. { en, en_US, en_GB, en_CA } are
...

In any case, the grub2 pkg should install a *complete* set of locales.