You think you can just get out of prison and use the money? They will be watching you and anything you buy with it or any cash you convert it to will be seized again. Might as well give it up for reduced sentence.
There aren't any nice places without extradition treaties where you won't be murdered by the people in charge, police, criminal gangs, et al. Or otherwise de facto forced to turn over the money for protection, after which you'll be discarded if you're lucky (and disappeared for convenience if you're not).
So I am unclear on this. In Germany or the US, if you rob a bank, hide the money, get arrested, and serve a X year sentence, what happens when you are released? Could you use the money? You have already served for the crime. I suppose they could keep some criminal charges in reserve? If nothing else, eventually the statute of limitations would kick in where the money is fair game? Just be sure to declare it on your taxes, lest they get you like Capone.
IANAL but I suspect this is the kind of thing civil forfeiture is originally intended for. You would have to sue in court and prove the cash was obtained through legal means.