As an add on to my question about pull down menus: I often wonder about the person making the decisions, which English was his/her birth language. I am a Canadian, living in Colombia, and I see quite a mix here, my daughter is learning English using a British text, she see TV from the USA and then there is me at home. All languages change from place to place but English must be the worst.
It is often said that Scottish Gaelic varies so much that one village in the island of Harris can't understand those from the next village.
This is of course a fiction! I suspect that non-speakers and langauge learners are partly responsible for the myth.
Most native speakers will rarely stop to notice regional variations. Learners, on the other hand, will often be defeated by this. There is probably no real alternative to trying to listen for and learn about the common differences (possibly outside of Duolingo - at least at the moment). A mix of dialects is possibly no bad thing.
It would be good if Duolingo could allow users to select a preferred target version of the language to be learned. However that is probably the icing on the cake, and there will no doubt be other priorities for the development team.