I don’t know German installation practice, so I cannot comment about whether he is right or not. I’ve looked here http://www.batt.co.uk/upload/files/din_copy2.pdf and from that, I seems that VDE 0100 is a standard for the erection of electrical equipment and the measures for protection against shock. It does not appear to be a standard against which equipment is manufactured, so my reading is, it would not be appropriate for the current transformer to be certified to that standard. But without reading the standard, I cannot be certain.
Provided that the extra low voltage cable out of the c.t. is adequately segregated from the other wiring, I don’t see where the problem is. The c.t. itself is CE marked, tested to 1 kV so it’s possibly against EU law not to fit it.
The SCT-013-000 data sheet says:
Dielectric strength(between shell and output) 1000V AC/1min
Fire resistance property: In accordance with UL94-Vo
You could try a German manufacturer of electrical instrumentation (Siemens springs to mind) and see if you can find a c.t. that either has a 1 V output (i.e. the burden resistor is inside the c.t. housing) or has a reasonably low current output, ideally 50 mA at your maximum current, though we can handle other currents with a small component change (though not 1 A or 5 A - due to the 3.5 mm jack connector).
I’ve looked at a few German c.t. manufacturers. C.T’s with 1 A secondary windings seem to be readily available. One of those would be usable, but you would need to arrange a 1.2 Ω burden resistor external to your emonTx (or emonPi) that’s rated at at least 2 W. You’d be able to leave the internal 22 Ω burden in parallel, the effect of that will be to give a resulting burden value of 1.14, which should be OK as far as the input is concerned, but will need a slight adjustment to the calibration (the difference from the nominal calibration is about 3.45%).