mark numbers as untranslatable

Change-Id: Ieb04f562e94ae4b8f09efbfeeaea7009c22322ff
Reviewed-on: https://gerrit.libreoffice.org/13253
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>