A small improvement of the upvote/downvote mechanism
A few times when I wanted to reply to a comment, I upvoted or downvoted the comment by mistake. The problem was, I couldn't undo the vote. Once I had upvoted a comment, clicking on the downvote arrow downvoted it. I could never get the vote back to neutral.
So Duolingo might consider the following change: If a user has upvoted a comment, clicking on the downvote arrow removes the upvote. Clicking once more on the downvote arrow will downvote the comment. Vice versa with downvotes.