Translation:Can this be a bit cheaper?
Yes, it's not due to lazy programming, but rather lazy brainstorming, if you want to find something to complain about :) The person who creates the exercise enters the list of translations manually. The mistake on their behalf could be trusting their own skill too much and leaving the exercise like that, instead of notifying the other contributors and asking them to brainstorm and add more translations (every contributor can). Or maybe really a bunch of people think about it and still they don't see some alternative translations, which is expected, especially if all of them are native speakers of Chinese but not English. You simply can't think of everything.... That's why the course is then opened in beta. Through the help of the Duolingo users contributors can be notified of errors and fix them. The mistake at this stage is that they publish a humongous amount of sentences right away instead of starting slowly. And since each one of them has some problem, it's virtually impossible to fix them all, even if learners diligently report and comment....
I know, I'm a contributor too :')
There's more than that it accepts typos (which is fine) but certainly strict with the only possible translation entries. If certain amount of people gets frustrated and check with forums the AI must have a way of learning from forum entries as well... What I mean we could make DuoLingo way better if we don't show of linguistic capabilities but easily contribute to a pool of translations and it could be democratised with votes and gamified with lingots etc.
It's nothing to do with programming. People who are probably not programmers have to enter each acceptable variant manually. Natural language processing is not at a point where you can just program stuff like this and have it work anywhere near as well as this, which as you've seen is far from perfect.
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The correct answer shown of "A little cheaper, ok?", and "A little cheaper, is that ok?" is wrong? No, it's not, it's fine. This, and the other acceptable English translations should be accepted, especially given the differences in grammar and word order between English and Chinese.
This is a poor question with current technology as there are about 50 ways to say this in English. Go the other direction into Chinese with building blocks or provide English blocks. I am a fairly high level of Chinese, and I have failed every attempt to place out of low level requirements because of the "type in English" questions. This seems like a problem that needs addressing.