One way to ease distinguishing between “i” and “í”
If you’re studying a language that has the letter í, such as Spanish, Portuguese, Catalan, or Irish, and you have trouble distinguishing between
í in that language because of the smallish diacritics in the Museo Sans Rounded typeface, and you use Duolingo in either Firefox, Chrome, Opera, Safari, or Edge, then there’s a way to ease distinguishing between these letters: replace the use of Museo Sans Rounded on Duolingo in your browser with locally installed typefaces of your choice. (Note that this method is not available with either the Duolingo apps or the Internet Explorer browser.)
First, if you use Firefox, Chrome, or Opera, the gratis Stylus browser add-on needs to be installed in your browser. (If you use Firefox 45.9.0 ESR, install version 2.1.1 of the gratis Stylish browser add-on instead of Stylus, since Stylus requires Firefox 48 or newer.) If you use Safari, install the gratis Stylish for Safari browser add-on from the Apple Extensions Gallery. If you use Edge, install the gratis Tampermonkey browser add-on for Edge. Once your browser’s add-on has been installed, restart your browser if required.
Second, install the gratis Replace Museo Sans Rounded on Duolingo user style in your browser. (If you’re using Tampermonkey in Edge, follow the instructions here to install the user style as a userscript.) This user style will only replace the use of Museo Sans Rounded on Web pages from duolingo.com; it won’t affect the text rendering of Web pages from any other site. The user style defaults to using the Verdana typeface family as a replacement, but if you find a different typeface family more to your liking, you can specify its names there before installing the user style. Note that no checking is done on the entered typeface names to ensure that they’re available on your device, so be sure that the entered names are correct. If you’d like to try different typefaces to see which family you like best, you can revisit the user style page and enter different typeface names to update the user style on your device.
Once the user style has been installed (or updated) on your device, it should take effect immediately; try opening a Duolingo discussion page to ensure that your chosen typeface family is now being used. If you find that a particular typeface family works especially well for you, please leave a comment here or on the user style page, so that others can try it too.
EDIT #1: Added information for installation in the Edge browser.
EDIT #2: Replaced reference to Stylish add-on with reference to Stylus add-on for supported browsers.
EDIT #3: A modified version of this user style needs to be uploaded to userstyles.org so that it can also replace DIN Next Rounded LT Pro, which is replacing Museo Sans Rounded on Duolingo, but at this writing [2019-03-31], that site no longer allows any of my browsers to access any of its pages.
I’m not familiar with what add-ons are available in browsers other than Firefox, so I thought that it would be best to suggest a method which would be applicable in the same way in multiple browsers.
Duolingo’s CSS shows that blocking Museo Sans Rounded would in some cases cause your browser’s default sans-serif typeface to be used in its place; in other cases, Helvetica or Arial would be used instead. (Their CSS even has a Japanese text section, in which メイリオ [Meiryo] or Hiragino Kaku Gothic Pro would be its replacement.) I thought it better to have a user-specifiable substitute typeface which would be used uniformly.