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Check the map in the FAQ-section, with that you can trace a route from Germany to Spain. Culture can only spread from one province to another. So if the Pfalz is your only province with German culture in your kingdom then you must first conquer a whole lot of other provinces before it can spread to Iberia.
No, Pfalz is the only county with german culture in my own demesne. However the vassals and subvassals of my Kingdom of Leon (and now Castille) hold an unbroken line from Pfalz to Genua and own Valencia.
