Having grown up in the UK and living in Australia, I do not find Americans polite. To me, politeness is "please", "thank you", "may I have", etc, whereas "I would like a latte today" reads to me as a demand. In context it's fine (it stands out a bit but not in a problematic way), it's not particularly rude, but in general just stating your desires is not considered polite in my experience in UK/AU.
There are some other parts of American English that may be considered polite, I notice a lot of US folks addressing me as "sir" for example, but this sort of thing comes off as insincere or even sarcastic/rude.
I know this is how people communicate so they don't really bother me, I'm used to them and accept that different people have different expectations. I also understand that Americans might believe they are being polite and consider me to be rude, but I think this is why blanket statements like "Americans are extremely polite" are just missing so much cultural nuance.
That's news to me! In my part of the world I call even the janitorial staff "Sir". I'm not aware of anyone ever thinking that was rude.
When an American says "sir" to me, I know I'm not in any of those positions, so it comes across as parody of those – highlighting the fact that I am not actually in the position of power, or that I am not a highly valued customer. In that way it's sarcastic, and it can imply that I'm actually imposing on the other person and taking that position of power, which as I'm not, therefore comes across as passive aggressive in a way.
If an American asked me to do something and I said "yes Mr President", arguably referring to the highest status in the culture, I expect it would be taken as sarcastic or rude, not polite, because the person is not in fact the president. That's sort of how I see it, but maybe this analogy doesn't work.
I've never ordered a latte "today".
A simple statement of "I'd like a latte" fits fine in our regional vernacular.
I think that "I'd like a latte today" would appear a weird bit superfluous of specificity, unless it comes from a regular and familiar customer who might normally order something different and/or random.
I mean: "Today"? As opposed to later this week or something? It's implicit that the latte is wanted as soon as they can get around to it. (Unless yesterday's order was something different, and then adding "today" may make sense.)
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But English is fucked up, and I'm getting old, so I've spent a lot of time observing (and sometimes producing) slight miscommunication.
In terms of things like ordering food or drink at a counter, it still works fine as long as nobody gets grumpy, and the desired item is produced.
I'm reminded of a local festival I went to as a little kid, with my parents, sometime. I was getting hungry and they were asking me what I wanted to eat. There were a lot of pop-up food vendor there, mostly with tables and stuff instead of the now-ubiquitous "food truck."
In the corner was a gyro stand with amazing-looking racks of spinny-meat. I wanted to try whatever that was.
The big banner said "GYROS" and we got in line.
Discussions were had between my parents about this "GYROS" concept, which they'd never seen before either. Was it a singular, or a plural? How many "GYROS" might a boy reasonable want? How was it pronounced? It looks like "gyro" as in "gyrocopter" but it seemed to them that it must be Greek, so they went through some variations on pronunciation as the line moved forward.
As we got closer, some of these questions were answered: The sign definitely referred to a plural offering, and seeing people leave it became clear that [unlike things like chorros or tacos or donuts] one was plenty.
And when we got to the front, the conversation went like this:
Parents: "Our son wants one of these... but we're not sure how to say it. Jye-roe? Hee-roe?"
"They're just gyros," he replied to them to them dismissively in a thick Greek accent, and motioned for his staff to produce 1 gyro.
And then the man looked at me, with his skin sweaty on that hot sunny day and a thick gold chain around his neck, and said to me in his very best and most careful English something to me that I can never forget. "I call them gyros. But listen to me, you can call them whatever you want. Jye-roe? Hee-roe? Yee-roe? Sandwich? Whatever you say, and however you say it: If you get what you expect, then you said it right. Alright?"
My trepidatious nods made sure that he was understood, and the awesome fucking sandwich-taco I had that day changed my entire perspective on food -- and ordering food -- forever.
So, sure: Ordering "one latte today"?
It sounds weird to me, but if it is understood and you get what you want, then it works. Correctness? Politeness? Whatever. Despite seeming weird: It works.
(Up next: There's a lot of ways to mispronounce approximately everything related to ordering pho, and none of them are wrong.)
To me (non-American) the above sounds like sarcasm, not politeness. Adding "today" and/or "actually" could mean you've had it with their delays.
I like to joke that Americans always seem to find ways to get offended by innocuous things, but in this case the joke is on me.
To me (Canadian, not American) "Could I get a latte today actually" sounded something like "Normally I get something other than a latter but actually today I would like a latte instead"
Not rude at all, but kind of assumes some context
To me it seems (without any context) that it might mean that you changed your mind about what day you wanted it. This does not seem to make sense in many contexts, though.
I stopped saying, stuff "I would like a latte today" or more Midwestern (could I get a latte today etc) in singapore because people would just get confused. Same with being too polite when recieving things. There's ways to be polite but it usually involves less words because anything else confuses people.