Poor translation of the politeness of ください.
The Japanese をください is being translated poorly, so that the politeness of the language is lost. For example, the course translates お茶をください as "Can I get tea?", rather than simply "tea, please".
"Can I get" is a far too colloquial translation, and not a particularly polite one.
Please reconsider the English wording.
I kind of think it is...
To me "Tea, please" sounds less than ideally polite itself. Dialect (and presumably culture more broadly) does play in here.
To me using "can" instead of "could" is probably a greater etiquette breach than omitting "please," which at that point can become redundant.
EDIT: to the person who downvoted me, presumably b/c you think your own version of polite is the only one out there, well, this is an international forum; we're not all the same; and dismissing an explanation of someone else's cultural experience - well, that's not very polite.
The rudeness is omitting the word "please." "Can I get tea?" and "Tea." are rude. "Can I get tea, please?" and "Tea, please" are polite. Small children are constantly reminded by their parents to always say "please" when asking for something.
I don't think it would be taken very well if I was a guest in someone's house and demanded 「茶をくれ。」 Saying "Can I get tea?" or simply "Tea" would be about the same.
If you were in a restaurant and the waiter directly asked you "Would you like coffee or tea?", or something similar, I would say "Tea, please". Otherwise I'd order with "May I have tea, please?", or "Could I have tea, please?". Using "get" in this context is a fairly modern usage and, while it is becoming very common in some areas, it's not at all polite English.
This is where culture plays in. I can't image a server ever asking "Would you like coffee or tea?" Maybe it would be used in the U.K. where tea is actually culturally important, but that's thousands of miles from here. And what has been arbitrarily codified as polite or not on a couple islands that far away (and possibly generations ago when it was "impolite" to speak in anything but R.P.) isn't of a great deal of interest to me in my day to day life in a different society with its own conceptions of politeness with distinct cultural origins.
お茶をください is "give me tea". This is polite enough when talking to a waiter, younger family, and friends.
The polite request is
which can be further adjusted for formality, all the way up to
or down to
Textbooks greatly oversimplify the politeness and formality dimensions of Japanese. There is a scene in Evangelion where the mission members come by to encourage the pilot who will be fighting the next day. Every one uses a different form of gambaru/gambatte.
Of course nobody says
or any of the other high-falutin' forms.
That's not entirely correct, though. ください comes from くださる, which is an honorific conjugation of くれる. Its honorific nature carries the politeness that isn't expressed in the translation given in this course.
Using "can" also implies it is conditional, which the original request doesn't contain. Therefore, it's a direct request in English, which in both cultures requires politeness. "Can I get tea?" is rude and abrupt. The fact that it's used colloquially and accepted in some places doesn't make it polite.
If you wanted a similar level of translation you'd probably use something like お茶頂戴.
I'm really thinking what's happened here is they're translating a direct request via a question in order to render the politeness. As a denizen of the Midwest, this makes a tremendous amount of sense to me. We don't tend to make direct requests for such things: with or without "please." "Please" simply isn't enough to make something framed as a direct request polite. Therefore, the translation is as a euphemistic question to make it polite. The problem is it's the wrong question (maybe it's the right one in Pittsburgh, where a number of the course creators seem to actually live).
Yes. If you think of the first part as what you are requesting, followed by をください to equate to the English "please", you're both correct and polite.
Whether you're responding to options or stating your initial want, the simple Object - Object Particle (を) - Action (In this case an honorific conjugation of "to give" that equates to "please" in English), makes it complete.
Here is a short article on the use of "Can I get" instead of "Can I have" http://www.macmillandictionaryblog.com/can-i-get
To me "can i get" just sounds quite uneducated as a request, but it is used more and more. "Could I have", "May I have", even "I'd like" are better ways to request, with an added please at the end being the best. I'm not alone: https://painintheenglish.com/case/230
The problem with all the "logical" arguments against "get" being deployed in favor of "have" is that it's trivial to construct the analogous ones for that verb, too:
Of course you can have cake. No physical impediments exist that would prevent your possessing cake, right? Now, what do you plan to do with it?
One definition of "have" is "possess", as you say. Another definition of "have" is "to eat or drink".
Still you are correct that logical arguments don't really work for language. If the usage continues to become more popular, "Can I get" may be the proper expression at some point.
I just came across this.. I think something that is being missed here a bit is that, while ください usually implies a fair amount of politeness, its use in the form of asking to be given something has become so ubiquitous and formulaic in modern Japanese that (IMO) it does not really convey any particular level of politeness anymore, by itself, when used in that way. I have actually seen real-world dialogue where 「...をください」 has been used to ask for something in the same sentence where the speaker is actually being (deliberately) downright rude to the person they're talking to in various other ways.
Really, the politeness of ください is something that can only be evaluated within context: sometimes it is very polite, sometimes it's not at all. To some extent, I actually rather respect Duolingo's tree for reflecting this reality better than many other language-learning resources I've seen.
Likewise, I think that leaving off "please" in English is not necessarily as rude as many people are making it out to be, but again this depends a lot on context. The biggest problem with Duolingo in general is that all of these sentences are presented with absolutely no context, so different people are going to read them different ways.
As for the use of "can I get" vs other possible forms, I really suspect that this is ultimately region-specific, and I'm not sure there's really a good answer that will please everyone. For some people, "can I get" seems horribly rude, and for others it's actually reasonably polite, whereas in some contexts, saying "tea, please" (despite using "please") actually can sound more rude than "can I get some tea". On the flip side, for some, something like "may I please have" can seem implausibly polite or even condescending.
I could see an argument in favor of a "middle ground" of perhaps using "could I get" or "may I have" instead of "can", as either would be both a bit more polite and arguably more grammatically correct. I do think any solution would probably need to accept all the different variations as valid, however, because depending on context any of them could be a perfectly appropriate translation.