mark numbers as untranslatable

Change-Id: Iaa592297e8a946c121b9eaedbbab136db7593316
Reviewed-on: https://gerrit.libreoffice.org/9838
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>