Have an are you sure button when submitting a very short answer.
Sometimes in my french I type J and then meaning to hit apostrophe to type J'ai I hit enter, which submits my answer to a question as J or something.. Maybe there should be something that checks this is the answer they want to enter if it is very short compared to how long it should be or something. I'm not sure if anyone else has this problem in other languages, and I find I don't do this too often and normally I just continue, but just as a thought, maybe this is something to consider implementing in the future..
I actually think its a good idea. I wouldn't want Duolingo to stop everything and work on this, but in the future if its not a huge undertaking its completely doable. They already have a check where if you by mistake enter the exact phrase instead of the translation, which some people do cause they start thinking in the other language or their own, it lets you do it over. So this which I imagine often happens can help out.
And I don't think learngood22 needs to be concerned, because it would only ask, are you sure, when the answer is much shorter than it should, which is very rare and when it does, a popup can appear to ask, are you sure, and then an, enter, for yes and maybe a space bar, for no. So learngood22, if you don't want to deal with it, it'll be just, enter enter, instead of just enter. Not even a second of delay.
I would also like a check for any of the words to be translated end up in the translation, because sometimes I'm so focus on words I'm having trouble with that I think in the other language as I translate and easy words come out not translated. Like I said, they already do this with the whole phrase, but a check when there is just one word not translated would be nice.