Related, on the country drop-down front: please put the United States (or whatever your customers' main country is) at the top. You can probably tell I want the US from a combination of, you know, 99% of your sales being to the US and my language being set to English. And, sure, put Canada and even the UK next to it. Go wild, have the top ten English-speaking countries there if you like! It makes things so much easier.
The trick, then, is that you don't remove anything from the alphabetical list. With modern computer technology, we can have two places to find something! So if I miss your fancy shortcut, or it's not applicable to me, everything will still be in the regular old familiar place. It just works.
This generates a really annoying features with some browsers. Suppose I want to select "United Kingdom". I open the drop-down and there are all the countries in alphabetical order, plus "United States" at the top of the list. I hit the 'U' key. It does not take me to the alphabetically listed countries beginning with 'U', it takes me to the "United States" entry at the top of the list. I might be able to type 'U-N-I-T-E-D-K' and get to the "United Kingdom" entry, but there are browsers where that does not work. (Nor does repeatedly hitting 'U' bring me to the later 'U' entries.)
Absolutely not. Language should never have any merit at all on country selection.
As a Swede that prefers the English language for tech and internet stuff, sites that try to be smart about country selection based on browser language or language selection based on IP location can kindly go die in a fire. An extra hot fire if they don't even let you manually override the automatic "detection".
That's why I also mentioned US companies with primarily US clienteles. I think that in that case, "browser is sending en-US language" and even say "IP geo-resolves to the US" is a strong enough signal to justify prioritizing "United States" in a country dropdown. It helps a decent fraction of your customers, and for the ones where it's wrong, they go from picking their country in the full drop-down to... picking their country in the full drop-down. The downside is microscopic on this one.
It's not evil like forced language/region selection with no fix available.
The trick, then, is that you don't remove anything from the alphabetical list. With modern computer technology, we can have two places to find something! So if I miss your fancy shortcut, or it's not applicable to me, everything will still be in the regular old familiar place. It just works.