Accent marks not easy to differentiate in this font
I'm having a hard time seeing the difference between the various accents in French in the font used. Even when I use the trick of control-+ to enlarge the font on the screen, the accents are quite small and not easy to distinguish. They are so short that the accent aigu and the accent grave look very similar. I know that at 46 my eyes aren't the best any more, but I can't be the only person who has trouble with this! :) I don't seem to have this issue in other French sites on the web.
I hope if you are considering any adjustments to the font you'll pick one that has clearer accent marks.
I have noticed this too, in both Spanish and French, that the accent marks are hard to distinguish. I think it is mostly the size of the font and the fact that it is black on gray instead of black on white.
It's dark grey on light grey in the box where it shows the correct solution after you make an error. And the corrected words are bold which makes it even more difficult to distinguish.
Spanish only has forward accents so I've only had trouble with i and í. But I can imagine that it might be difficult to distinguish between á â and à in the blurry bold grey on grey.
I have actually not had any problem distinguishing accents myself. Maybe I have amazing eyesight!
I've noticed this on other sites, maybe it's a standard font and we need a better one.
The font used is the first of the following that you have installed on your system: Helvetica Neue, Helvetica, Arial, [your default sans-serif font].
Helvetica Neue is better than Helvetica (although readability-wise still worse than Tahoma) but unless you're using a Mac you probably don't have it installed. So in all likelihood, it's Helvetica that is the culprit.
I agree that the aigu and the grave are hard to distinguish. Although the tiny font size has something to do with it, at the same size the accents in Arial are pretty clear due to their off-centre placement. And Tahoma is even easier to read. I have zoomed in a little, but cannot zoom beyond 125% because Duolingo doesn't adapt properly.
Another problem that I have with the font is that when I zoom in I seem to be experiencing hinting issues. For example, the E in your post has a one pixel middle bar, but two pixel top and bottom bars. Another problem is features not lining up letter-to-letter which creates an uneven inconsistent look.
On a related note, I think Duolingo could be much more economical with screen space, which in turn would allow it to use a much bigger font. It is madness that we're even discussing this. How can we possibly have trouble fitting a few lines of text on a screen that is bigger than A4?