[Arran]

Well, it was always 50 Hz when it eventually standardized (I understand when they first started the electrification there was no standard, and they used whatever, and there were DC mains, AC mains, 30V, 50V, 120V and such, and I suspect the frequency was not an issue - the main goal was the electric lighting).
Never really 60Hz, like it is here/

But, to tell you the truth, 220V is more convenient - you don't have to handle as much current, though it is deadlier, of course. But then to plug in an electric teapot that is 1 kWt of power, would take me to provide for a 4.5A wiring there and for 9A wiring here; there go your losses, flammability etc. (not that we had less fires that you do - probably more; Russians are notorious for their no giving a crap attitude when something goes bad, waiting for a disaster to happen, and they used aluminum wiring up until very recently, 80-s/90-s, whereas here it was outlawed way before, and people stopped using it even before that. And, what's worse, there are still places with it over there, as no one is required to replace it; just recently an acquaintance of mine from Moscow complained about two small fires one after another started in the outlets, and I told him that the wiring is probably aluminum and that was the reason, and he confirmed, that it was the case - the wiring there is aluminum. And all they did was replace the outlet, clean the wires and close it. There. )

As for the plug in Europe, I understand it is more or less standardized (one of my projects was a power supply that would work in there), or at least there is not as many varieties as there used to be.

The distance between the prongs is the same, but there is a GND plug, or GND ring, and most differences are still in the Eastern Europe where they had their own thing before 90s.

Russian plug used thinner prongs, and never had a safety GND, unless a specific plug was used (for heavy equipment, like electric washers, and then it was nothing like you've seen in appliances - flat prongs at 120 degree angles to each other), so it would fit a European outlet, but would be loose in it.

Also we used bare non-plated brass for the prongs.

There are some houses that were wired using aluminum wire in Canada, mostly from the late 1960s to mid 1970s, after that it was banned for new instalations. However if the wiring was installed before the ban you are allowed to keep it but anything that gets replaced must be replaced with copper, not that you can find aluminum 14/2 or 12/2 house wire anymore anyhow. Where the aluminum wire becomes dangerous is when people use outlets, switches, and wire nuts that are rated only for copper and the connections oxidize and heat up.
Knob and tube is a different story, if your house has knob and tube style wiring, the kind with single conductors and porcelain insulators, it must be replaced when the house is renovated. Knob and tube has no ground and the wires are spliced, soldered, and taped together without being housed in a junction box, the insulation was cloth covered rubber. The splices break down over time, get hot if something is overloaded, and then can cause fire since they are not housed in a box.
I understand the advantage of using a higher voltage for supplying an appliance of the same Wattage, you can use wires of a lighter gauge, this was in part why most auto manufacturers switched over to 12 volt electrical systems from 6 volt in the mid 1950s. However I also figured that it took more energy to supply a higher line volatage, not to mention the shock hazzard is greater for insulation of a different type. Most of the Americas use 120 volt line voltage down to South America, there one half of the countries use 120 volts and the other half use 240 volts. I guess the electrical grids were set up by U.S engineers in half of the countries, and British and French engineers in the other half.
One thing that was not standardized here was the line frequency, most places had 60 cps but there were many that had 25 cps especially in Canada. In some U.S cities they had 40 cps and some used 110 vdc mains. In theory the line voltage was supposed to be 110-120 volts, in practice it varied from place to place, day to day, and one time of day to the next, it could be as low as 105 volts and as high as 125 volts especially back in the 1920s, some radios had taps on the power transformer for this and others had a ballast. In the 25 cycle areas it was supposed to be 115 volts.
Getting back to the outlets used I know that the French, Italians, British, and Irish each use outlets of their own design. Many of the other countries use German style Shucko (sp) outlets where the outside of the plug fits into a round socket. The Australian outlets look like an older American 240 volt air conditioning outlet with three slanted blades, it comes in handy in the rare event you end up with a radio from there.
Regards
Arran