Idea: New bar improvement
Not sure if this ha already been implemented but to cut it quick, having correct grammar (using the tildes and errr correct letter things lol) should fill the bar up with a lil more juice than if you typed the correct answer using only your english keyboard.
Honestly, that should really be the standard, so answers without any errors (perhaps with the exception of punctuation), whether by neglecting to use diacritics or just spelling errors in general, should just fill up the bar with the normal amount that it's giving now, and an answer containing an error might only give you half credit. What's most important is that students are encouraged to write properly from the start. Maybe Duolingo could give a short tutorial on how to set up a new foreign language keyboard on one's PC or Mac to each student starting a new language, even before the basics. If you already have the keyboard, you could just skip it. I think this kind of approach is especially essential when the base language uses a different writing system than the target language, as is the case in several current and future courses (English>Russian, Hindi>English, Japanese>English, etc.).