You shouldn't have problems with getting around using English in Warsaw.
I would support the idea of bringing this still exotic place like Warsaw(or Poland in general) closer to the general public. Yes, there is Prague or London or Berlin which are all lovely places, but Warsaw is nice too and still not discovered by so many people. It's not that far from Europe and those coming from US - if there will be any - are going to have jet lag anyway, be it London or Warsaw.
What Warsaw has in return is a non limited, constant, never-ending stream of best vodkas in the world
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