Not many people have heard of it for whatever reason, but what you're describing can be accomplished perfectly well on X11 systems using XCompose: https://wiki.

Not many people have heard of it for whatever reason, but what you're describing can be accomplished perfectly well on X11 systems using XCompose: https://wiki.archlinux.org/index.php/Accents_on_US_keyboards https://wiki.archlinux.org/index.php/Accents_on_US_keyboards