It seems to me that creating the QT_QPA_PLATFORM environment variable early enough in main.cpp just _might_ be working. It's just very hard for me to test without an actual international keyboard.
@BeckyEbook: can you try inserting the following line in main.cpp at line 363 (just before the MainApplication app(argc, argv); line):
Code:
qputenv("QT_QPA_PLATFORM", "windows:altgr");
And see if it works for you? Make sure you run Sigil without the -platform windows:altgr parameter.
I don't want to play around with ifdefing for Windows and creating new preference settings if it's not going to work.