Umm, just as with any other expensive property - they ask you to declare them; and if you conveniently forget to declare it, but at some time later (say, after 5 years) they somehow find that out, then you go to jail.

Are you sure that you can hide that stash (and all purchases/deals made from it) permanently?

Just until you ditch citizenship of that prison country and live happily ever after spending your bitcoins in Germany or some warm paradise.

Germany treats BTC income the exact same way.

Thank you. I haven't researched the subject. I still think you will be better of dealing with German tax authorities than with IRS. I suspect there are and will be some European countries that treat bitcoins with more leniency.