It's not impossible but there are two principal difficulties:
Firstly, the satellites that beam the signals down to earth have fairly tight 'footprints'. That means that as soon as you get beyond the 'inner core' of the signal, you rapidly start needing larger and larger satellite dishes. See here:
http://www.satcure.co.uk/2d/2d_footprint3.gif
For reception in, say, Berlin, you'd probably need a 1.5m dish. Such a dish costs a lot more than a standard Sky dish. Additionally, here in the UK, a dish of that size requires planning permission. (I don't know whether the same applies in Germany but it would need to be considered).
Secondly, Sky don't have the broadcasting rights to offer a service to Germany. This means that you can't register an account there. You have to register an account at an address in the UK and then get the card sent to you.
If you Google 'Sky TV Germany' you'll find firms which offer to register an account in the UK and provide you with the card. (Some might also supply a suitable dish and receiver). They claim that the service is legal but I'm sure Sky would disagree. (Such firms tend to be short-lived, which suggests that they're being subjected to successful legal challenges or that disgruntled customers are getting them closed down).
Chris