The mechanical vario is mandatory as per EASA glider certification (as mech. anemometer, mech. altimeter and mech. compass). The electronic vario is usually linked to the computer with many other features (final glide, etc...).

For my LS8 the vario is not listed as minimum equiptment. I have the new Air Avionics electronic altimeter which is ETSO certified and complies with the requirements stated in the LS8 maintenance manual.

I was not able to find any regulations prohibiting electric minimum instrumentation in EU or German national law. Do you have any reference to support your statement?