simon provides the possibility to simulate user input like keystrokes or mouse clicks.
This functionality is provided by the simoneventsimulation library. The library internally uses plattform dependant backends for X11 (xtst) and Microsoft Windows (WinAPI).
The backends need to provide a common sendKey(unsigned int /*unicode*/) method mandated by the shared interface. Since neither Xtst nor WinAPI provide a way to "write" such a character directly we first need to find out how the user would generate such a key.
Internally both methods use a simple switch / case to first determine if this is a special key (like the "Home" key) and if not try to dertmine the keycode by extracting the "base character" (for example: The base character of € is e) and then trying to find out which modifiers (shift, altgr, control) were pressed to get to the keycode given.
This works fine for "normal" characters and special characters like €. However one group of "keys" is missing: The dead keys.
Dead keys are used to generate characters like â or é. They are generated by first pressing one key like ^, releasing it, and then pressing the next key. This is substantially different from modifier keys as there the modifier key is not released until the combination is complete.
This is why simon in the current form does not know how to handle characters that need dead keys. I hope to get this integrated before simon goes stable as this is a substantial feature for languages like French.