From experience, I'd like to add that the myth of "once it's below -X it doesn't really matter" is just not true. -50F feels WAYYYY colder than -25F for example.
Measured temp is one thing, wind chill is another.
But it is indeed often quite windy.
And I slept outside in temperatures colder than this, my children did, and their children eventually will. It's a matter of proper clothing.
But in Danish, 70 isn't syv-something. Instead it seems it's halvfjerds, which sounds like half a fjerd, except a fjerd is not a number. ;-) And even more confusingly, 50 sounds awfully like half-60.
From what I've read, it used to be "half four twenty" (halvfjerdsindstyve), where "half four" is an archaic way of saying 3½, so 3½ 20 = 70. Which later, I suppose, got contracted into halvfjerds. Admittedly you can just treat them like opaque symbols to memorize, so I doubt anyone thinks of 75 as "5 and 3½ x 20". But the Norwegian numbers seem more orderly...
Of course, English used to be like this too — thus "three score years and ten". And many languages still retain non-decimalised words for eleven and twelve (and sometimes powers of them, like a gross or mass.)
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[1] Well, French French. Swiss French and Belgian French are much more sensible.
My experience is that this is true in the long-term, but if you're only outside for a few minutes, you won't notice the difference unless it's windy.
Yes, wind... enough wind can ruin your day at any temperature.
Today it was -3C but very windy and dry it felt like -50C after coming out of a warm office!