I always get that I should pay attention to the accents, when I have to type special charachters, but in this type of task there is no keyboard below the input box with the necessary charachters. As a workaround I saved these charachters to file so this problem does not got me, but I would appreciate a fix.
Unless you add Czech keyboard to your computer (which is easy but it may take time getting accustomed to how to use it), Duo does not support Czech characters when translating to English. That is why we accepta MATEJ, KATERINA, etc. without the accents on this side.