The French lessons do not recognise the "Ç" accent
I have been going through the French lessons and apparently, whenever I put the 'Ç' accent, it always shows me the pop-up telling me to 'Pay attention to the ç character'. Hence, it does not recognise it. Thought to take my duty as a tester seriously and report this :)
I don't have this problem. Just checked it with garçon in the first lesson of the French from English course. Then I thought maybe it's only a problem with the capital letter. So I went to Lesson 1 of Common Phrases (where ça is introduced) and wrote "TU MANGES ÇA" in a dictation. Duolingo did not complain.
My setup consists in using the Duolingo website (not an app) with Firefox on Linux and with the US-International keyboard layout. I entered ç once by clicking it on the special characters box below the text input field, and once by pressing AltGr plus Comma. For Ç I only had the latter option (plus Shift, obviously) because it's not on the special characters box.
What setup are you using? How do you produce the letter?