The Leica C-lux file on raw.pixls.us does not open in darktable. So if you want support there, create an issue here (Issues · darktable-org/darktable · GitHub) and provide a sample of your camera to https://raw.pixls.us
The file does open in RawTherapee. The only thing that is needed is a proper color calibration. For that, please follow the steps on RawPedia as I have pointed out already.