There is some Polish in there too, but it's more minimal than German or Russian, I think. Not a true scholar on the subject by any means, so I could very well be wrong.
You're point about the migrations to Eastern Europe is well-taken. Interestingly, one of the theories (and it is only a theory as far as I know) about why Jews were involved in moneylending and other capital-intensive industries has to do with the fact that Jews were forced to migrate so often. Because they might be forced out of an area at the drop of a hat, they couldn't afford to have heavy merchandise that had to be loaded and transported quickly. Rather, they could only take what they could carry or load quickly, and money was often the easiest item to move and had currency everywhere.
There are of course other equally plausible factors that could explain it, either in whole or in part (the Christian prohibition against usury comes to mind), but I think it's an interesting theory nonetheless.
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