In the lessons, there is a tool for entering special characters such as the upside down question mark in Spanish or the umlauts (ä, ö, ü) in German. So far, I haven't found anything like that in the "Questions" section. Am I missing something? If not, it would really be great to have such a tool in the "Questions" section, too. :)
Thankfully there are also Alt-Codes (codes that you type in a numpad while holding down the alt key) that would be awesome if DuoLingo could provide such information when hovering over one of the symbol buttons on an input box.
Actually, I'll go create a separate discussion and see if I can get some feedback from the devs. If you agree and want to support it, you should go to the discussion page and upvote it so it gets noticed :-).
Discussion Page: http://duolingo.com/#/comment/171282
Also has edits for those of you on Mac / Linux
Thanks to you both! Elae, I mentioned the German characters just as an example. :) I got them on my keyboard, so that's fortunately not a problem for me (though it might be for other learners). However, I don't have many of the Spanish and the French characters, which is rather annoying at times. Maybe I'll try Kelvinsong's suggestion. PS: "ß" can be replaced by "ss" ;)
I found how to type them directly on my keyboard, it speeds up my lessons a lot.
For example, here is a page for how to do it on a mac: http://tlt.its.psu.edu/suggestions/international/accents/codemac.html
Your fingers quickly learn the combos and it is much nicer than the tool in lessons.