Dead keys used to work as they should until months ago but since whatever update of my debian/gnome/whatever I fail to both type ñ and to find a solution. I live in Viña, Chile, so it's not so uncommon that I need this :( Typing ´ and e is é as it should. Typing altGr and S gives me Ş as it should but typing altGr and n gives ~n and not ñ as it should. It worked before and I can't find any setting and neither can I believe this is not a huge issue to others.
My keyboard layout is "German". gnome-control-center -> Keyboard has very limited settings. Typing (Repeat Keys and Cursor Blinking) and Shortcuts. There is nothing on 3rd level key as suggested by terdon.