"Chinese" vs. "Mandarin" and "Cantonese"
I believe that in the case of Chinese language courses, they should not be called "Chinese," but rather Cantonese or Mandarin for clarity and for the purpose of being able to expand Duolingo to offer both.
I don't think it's a problem so long as the course is clear about what it's teaching. There is a general expectation that "Chinese", in the context of a language course, refers to Mandarin. It may help to see the point if you consider that there are people who insist Spanish courses should be called Castilian courses because there is also Catalan. (I am not saying it's the same thing. Obviously there is a lot more justification to be explicit about Mandarin than about Castilian.)
I get that. I think people are stupid when they say it should be called Castillian, because you will always hear people say "Spanish" while meaning "Castillian". But will NEVER hear anyone say "Spanish" referring to Catalan, Basque or Galician. It's just pretentious. However, when it comes to Chinese, I can totally get why they say it should be explicit which language they're teaching, beacuse people do use the term "Chinese" interchangeably to mean both.
There are several dialect groups in China, such as Mandarin, Wu, Gan, Xiang, Min, Hakka, Yue (including Cantonese). And Mandarin is also called standard Chinese, which is spoken by most of Chinese people. So if duolingo offers Chinese course in the future, it would be probably Mandarin. There are more information on wikipedia. http://en.wikipedia.org/wiki/Chinese_language
Yes, that's true! I only simply meant to make a small statement about their similarties and differences. My main point is that I don't think there is any specific need to change the course title until necessary to point out the differences because there are two Chinese courses. :)