Hello,
I recently faced problems running GUI tests on Jenkins on a Linux slave using XVFB. The linux was configured in French, but XVFB in english, and I did not really understood what was happening and why the wrong keys were being sent (I received "&" instead of "1" for instance in textfields).
I finally understood the auto-discovery of KeyStrokeMappingProvider through Locale but it did not work correctly for me either. Finally, I hacked through your sources to add a command line property (like -DKeyStrokeMappingProvider=KeyStrokeMappingProvider_en on the command line) to be able to force the "en" Provider and bypass the auto-detection.
So my suggestion is to be able to override auto-detection. I can provide a patch if you're interested (please tell me the way you see it).
Regards