UK vs. US date formats
Some of the translations switch to a US date structure, i.e.. September 19th, while others stick with the European (?) structure, ie. 19 September. Both ways are correct, but the overall translation with a whole list of dates is going to look very odd if the date format isn't consistent throughout.
I have the same concern. In the article I'm translating now, there have already been a few little edit wars over date formats, and the translation currently has several different formats. I'm not going to change any now, since it seems pointless to try to win all the wars over individual sentences.
Maybe there's some final edit phase where things like that can be cleaned up.
But it would be good to have a "ruling" from Duolingo over how to format dates in the translations. I wonder if it could detect dates, and pop up a dialog recommending how to do it. That would probably put a stop to 99% of the date-format edit-wars.