I want to know the answer to the following question:
When did cities like Diventer and Zutphen start becoming more linguistically diverse?
All the background I'm provided with is that "From the 14th to 15th century onward, its urban centers (Deventer, Zwolle and Kampen as well as Zutphen and Doesburg) have been increasingly influenced by the western written Dutch and became a linguistically mixed area.". Is that enough to answer the question?
Answer: yes