At 20 letters it's a suitably 'difficult' word even if it were actually an English one with familiar pronunciation. It being a German compound word makes it's usefulness to the general English speaking population highly questionable.

I would bet money that 2/3 or more of the people I know, keeping in mind that my technical acquaintances are only a small fraction, don't know Zeitgeist enough to pronounce it properly or even give a definition for it if asked.

Edit: Same goes for Schadenfreude