[Printing-architecture] How to request "Media Limits: ..." on job-sheets to print mm instead of inches?

I have a print queue installed via "lpadmin ... -m everywhere". This
auto-generated a PPD with a line for the printable area saying

   *ImageableArea A4: "11.990551181102 11.990551181102 583.285039370079
829.899212598425"

When I request job-sheets to be printed the respective line on the printed
sheet reads

   Media Limits: 0.17 x 0.17 to 8.10 x 11.53 inches

What should I do to get this Info given in millimeters instead of inches?

I tried adding a line of "DefaultLanguage de" to cupsd.conf and restarted
the service. But this didn't change the printed line on the job-sheet (not
even the English *"Media Limits" *changed -- but I do not care so much
about that).

P.S.: Is this currently the right forum to ask such questions? I searched
OpenPrinting's github, but couldn't figure it out there, and I didn't want
to open an issue (yet).

Thanks, Kurt.