each of the native launchers:
linux/native/jpackageapplauncher/launcher.cpp,
windows/native/jpackageapplauncher/WinLauncher.cpp, and
macosx/native/jpackageapplauncher/main.m
contain the line:
setlocale(LC_ALL, "en_US.utf8");

We need to investigate if this is needed, and this means for a user whose desktop is (say) German, or French, or Japanese ?

We also need to verify that when the Java app is launched from this environment it is not inheriting this US locale.