i or í
Is it possible to use a font that either has an "i" with no dot, or longer accents? (or both?)
Yeah, those two can be pretty difficult to distinguish. I don't know if DL is able to combine different fonts in a single course (more prominent fada for Irish, regular font for English), but I doubt they can, or even want to switch. The current font can't even handle Šš Đđ Čč Ćć Žž without reverting to a serif font; for a site that invests a lot in its design and appearance, this looks incredibly sloppy, but they don't seem bothered by it.
The shame of it is that this typeface, Museo Sans Rounded, does support those letters.
Museo Sans Rounded is not well suited for distinguishing “i” from “í”, particularly at smallish sizes.
The lower-case a on the sign in that picture is a bit jarring — it looks narrower and slightly smaller than the other rounded letters, and the kerning to the left of each a has suffered as a result.