Allright. After flashing way back to RX-34_2007SE_4.2007.38-2 and installing Xkbd, it works just fine.

All keys are recognized and correctly displayed when typed as expected it would. No weirdness at all.

So what might be a program, file or database that I can copy over to Diablo from the first OS version that might finally fix Xkbd once and for all?

Even a guess on this would be helpful for me.