Displaying 8-bit charaters is easy. You can use them just as you would use 7-bit ASCII. Getting applications to accept input of special characters is an entirely different matter.
If you are using e.g. the Xt toolkit and a widget set like Motif you need only add one line to your program. As your first call to Xt use XtSetLanguageProc. Like this:
int main (int argc, char** argv)
{
...
XtSetLanguageProc (NULL, NULL, NULL);
top = XtAppInitialize ( ... );
...
}
Now your program will automagically look up the LC_CTYPE variable and interpret dead keys etc. according to the Compose tables in /usr/X11R6/lib/X11/locale/. This should work for all Western European keyboard layouts and is entirely portable. As XFree86 multilanguage support gets better your program will also be useful in Eastern Europe and the Middle East.
This method of input is supported by Xt, Xlib and Motif v1.2 (and higher.) According to the information I have available it is only partially supported by Xaw. If you have further information on this subject I would like to hear from you.
This section was adapted from a more extensive discussion in Michael Gschwind's Programming for Internationalization. See section Other documents of relevance for a pointer to that document.