This might seem as duplicate of Pressing key with accent character makes it enter twice but it is not:
About three days ago, the issue started - I am using Slovak (Slovakia) keyboard, and the key for adding accents/diacritics (just left from backspace) acts strangely - it should "do nothing" upon pressing, and then when character key is pressed right after it, it should output that character with accent/diacritics.
However, in most programs, pressing it once results in immediately outputting the accent itself twice (which under normal circumstances happens when you press the key twice). This issue doesn't happen in Visual Studio or any program I make in it, and Pidgin, it seems to happen everywhere else (firefox, notepad, MS OneNote, Windows Explorer itself).
I am not aware of any software installations, driver changes or system updates between the time it worked properly and the time when it broke.
What could be the problem and how do I solve it?