Germany 3 phase because you can use 4 wires of small diameter for the supply, and the load is going to be balanced down the street line, so you can use a smaller diameter neutral, as the current it has to handle is only the imbalance between phases, not the full phase current. Thus a lower cost of copper per house supply for the same power level, plus your distribution system has a large copper saving in smaller neutrals. the inherent balancing of load is also good for the supply side, less draw on one phase with peak cooling time is balanced down the street, and all loads are not on a single phase.
UK uses ring mains, because of history, and they will not change, though the wire sizes have changed over the decades as cable insulation improved, the original cables used DCC gutta percha tinned copper, and a ring main would have been a 4mm cable, but the high temperature rise allowed on new PVC insulation means the cable size was relaxed to 2.5mm later on.
The silver wire was used in the Manhattan Project, as they needed massive electromagnets in the early isotope separators, and copper was a war resource and scarce, so the US Mint loaned them hundreds of tons of silver, which was used to make wire used to wind them. Slight power saving as it had lower resistance, and after the war the silver was returned ( which is why none ended up as museum pieces) with only a small loss from all the processing and recovery.
Wire nuts here in South Africa are not a plastic nut, but a ceramic unit with a thread formed in the inside, so you can twist the wire into them, and even in a fire they will not melt before the wire, even if they arc the cable melts first. Pretty reliable if applied right, like any other connector, and as before, differs per country. All sockets here and switches are not allowed to be push in, you have to have a screwed clamp on the wire, though the Wago style is becoming popular for joining cables in the junctions. Preferred though is a crimped ferrule and an insulating sleeve over it, used mostly on larger cables 4mm and higher, as that is the only method allowed other than a screw connector.
Copper coated aluminium is very common, often used in windings of transformers, because it is cheaper, even if it has issues with creep and low melting point inside windings. If you have a newer microwave, new home appliance with an electric motor or any mains frequency chokes or transformers it is likely to be wound with CCA wire. A lot of the cheap premade cables are also that, or even copper coated ( hopefully) steel, or even some mystery wire of indeterminate type, most likely made from poor grade recycled metal. Buy a cheap set of jump leads and they are almost sure to be a CCA core in a very thick foamed plastic cover, so that they look like high capacity, but which are not even going to pass 10A without overheating.
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