The ground wire was so poorly screwed in it came out at the first tug.
In theory Austria followed the German color coding, but in fact conduit installs used whatever color was handy for phases (and often neutrals too). It isn't all that unusual either to find the circuits color coded, i.e. one circuit hot and neutral blue, the next both wires black, the third white, the fourth yellow and the fifth purple. So the three blue phases don't really surprise me - theoretically blue was the color of the second or third phase depending on the type of cable used (4w had the order black-grey-blue-red and 5 wire had black - blue - black - grey - red).
That sheath was just some purple tubing that extended from the socket into the conduit and must have been quite common back then (also came in various colors). That stuff was for example also used where sockets were installed in a panel to protect the conduit wire running from the Diazed fuses to the socket.
In one apartment I also saw a strange setup where a switch would select between either washing machine or dishwasher and the conduit wire to the dishwasher entered said switch in similar tubing.
The guts are held to the casing with a long screw and I suspect it goes directly into the earth connector. You can see that brass screw in the second picture.
I also posted these pictures on a German board and no one has ever seen anything like this.
In some ways it really looks like a predecessor of today's CEE plugs. The "typical" 3ph plugs back then were either 3 pins in a row and scrapers for earth and neutral (or just earth) or 4 pins in a row for 3ph and earth (pretty dangerous since the pin layout was symmetric and some of them could be assembled 180 degrees turned... so the ground and grounded plug casing became hot...). Though there were other systems that had one pin offset to prevent this... or another system with 5 pins in 2 rows... and all these contraptions existed in various sizes.
For example, the one with 4 pins in a row exists in 15A, 25A, 40A and 63A versions. The 25A version was pretty common in rural locations, as was the 3 pin + scraper. At some point the whole caboodle got outlawed since they wanted to phase out any metal plugs and sockets.
The GDR circumvented that intention by producing aluminium CEE plugs and sockets... and some of those still exist. On the other hand, many of the older metal plugs are still around too.
