Adding Character Accents in XFree86?

debrain asks: "How does one access accent characters (such as tilde, grav, acute, etc.) over normal characters in XFree86? I am quite good with Linux, X, and the like, but I have never found a *good*, *simple* way to do this. Some programs have post-character keystrokes, such as 'a' followed by 'alt-g' or some such, but is there a consistent way to do this, without hacks such as 'dead keys' in XFree86?" A system-wide facility for entering such chars would be a nice thing, if it does exist, then please share the info. Most apps have their own handling for these special characters. What applications do have keystrokes that allow you to easily add character accents, and if you were to design a system-wide handler for such, how would you do it?