Please add a "virtual keyboard" for each language.
Several users are looking for workarounds for typing umlauts in German and accents in French and Italian instead of using the mouse to input these special characters (frustrating when trying to do a timed test.) Various solutions exist for Windows and Mac, and none are very elegant. There is one elegant solution, though, and it can be executed within the application so that all users can use the perfect keyboard for the language they are trying to learn regardless of which computer they use.
If you look at Google Translate, you will notice a keyboard icon in the lower left-hand corner of the box on the left. Click that icon, and a virtual keyboard will pop up on your computer screen below that text input box, and the keys will mirror the layout for whatever language is selected. Any press of a key on your physical keyboard will be reflected graphically on the virtual keyboard, making the new layout easier to learn. You can click and drag the virtual keyboard to any part of the screen, and if you don't like it or need to get rid of it to type with your more familiar keyboard layout, simply close the virtual one.
I know this isn't a general purpose solution, but, for Windows users, the "U.S. International" keyboard layout in Windows (should already be built-in, select it from the control panel) actually works exceptionally well. It uses various "dead keys" for typing special characters. For umlauts, one would press the double-quote key followed by a, o, u, A, O or U and it would print an umlauted equivalent. There was a similarly convenient way for typing eszetts. The single quote acted as a dead key to those letters that required accents instead of umlauts, and the tilde worked for characters like "ñ". The characters on the dead keys themselves could be typed by pressing the dead key (single quote say) followed by a space. This was all very natural and easy to use, and I'd recommend it to anyone here using Windows.
Unfortunately, I'm on Linux, and, although there are international layouts for Linux, they suck by comparison.
Thanks for the recommendation, chubbard, I think I might like that solution more than selecting a purely German or French keyboard via Windows. I'll give it a try. I know that the development team for Duolingo must be terribly busy, but I do think that a "soft" keyboard would be a big help down the road. It can just be an icon offering the option of a different language keyboard when clicked, and people on Linux or Mac or Windows or an iPad or whatever can use that keyboard. If one does not want to use it, one simply doesn't click the icon.