mark numbers as untranslatable

Change-Id: I644f0df042dcf414b85514d5edb05cecc8f1537a
Reviewed-on: https://gerrit.libreoffice.org/10711
Reviewed-by: Joren De Cuyper <jorendc@libreoffice.org>
Tested-by: Joren De Cuyper <jorendc@libreoffice.org>