According to this article, they produce in fourteen countries:

‘Productie gebeurt in veertien landen; Boska heeft twee ’eigen’ fabrieken in Polen en China en twee sociale werkplaatsen in Nederland.’ (‘Production is done in fourteen countries; Boska has two ‘own’ factories in Poland and China and two social workplaces in the Netherlands.’)

But if they’d mostly produce in the EU, they’d probably advertise that, and they don’t mention anything on where their production happens on their site.