https://invisible-island.net/xterm/xtoolkit/
XtSetKeyTranslator, XtTranslateKeycode, XtRegisterCaseConverter,
XtConvertCase - convert KeySym to KeyCodes
#include <X11/Intrinsic.h>
void XtSetKeyTranslator(Display *display, XtKeyProc proc);
void XtTranslateKeycode(Display *display, KeyCode keycode, Modifiers
modifiers, Modifiers *modifiers_return, KeySym *keysym_return);
void XtRegisterCaseConverter(Display *display, XtCaseProc proc, KeySym
start, KeySym stop);
void XtConvertCase(Display *display, KeySym keysym, KeySym
*lower_return, KeySym *upper_return);
display Specifies the display.
keycode Specifies the KeyCode to translate.
keysym Specifies the KeySym to convert.
keysym_return
Returns the resulting KeySym.
lower_return
Returns the lowercase equivalent of the KeySym.
upper_return
Returns the uppercase equivalent of the KeySym.
modifiers Specifies the modifiers to the KeyCode.
modifiers_return
Returns a mask that indicates the modifiers actually used to
generate the KeySym.
proc Specifies the procedure that is to perform key translations
or conversions.
start Specifies the first KeySym for which this converter is valid.
stop Specifies the last KeySym for which this converter is valid.
The XtSetKeyTranslator function sets the specified procedure as the
current key translator. The default translator is XtTranslateKey, an
XtKeyProc that uses Shift and Lock modifiers with the interpretations
defined by the core protocol. It is provided so that new translators
can call it to get default KeyCode-to-KeySym translations and so that
the default translator can be reinstalled.
The XtTranslateKeycode function passes the specified arguments directly
to the currently registered KeyCode to KeySym translator.
The XtRegisterCaseConverter registers the specified case converter.
The start and stop arguments provide the inclusive range of KeySyms for
which this converter is to be called. The new converter overrides any
previous converters for KeySyms in that range. No interface exists to
remove converters; you need to register an identity converter. When a
new converter is registered, the Intrinsics refreshes the keyboard
state if necessary. The default converter understands case conversion
for all KeySyms defined in the core protocol.
The XtConvertCase function calls the appropriate converter and returns
the results. A user-supplied XtKeyProc may need to use this function.
X Toolkit Intrinsics – C Language Interface
Xlib - C Language X Interface
X Version 11 libXt 1.1.5.2 XtSetKeyTranslator(3)