alt Hacker NewsNon latin characters are sometimes inputted by holding down a key. For example on my keyboard holding down z shows ź,ž and ż with a corresponding number to select which one I would like to type. I haven't checked but one would assume if you're detecting keydown the input at that time will be z, and keyup would record ž (or whatever was selected).
Physical keyboards and virtual keyboards are different. Traditionally, ź and ż (my keyboard doesn't have ž) are inputted on keydown X or keydown Z while Alt modifier is active.