"If you understand the culture of a country, you will be prone to knowing what its people have said." (Or, "what its people say".) "A country" because I have no idea which country you mean. "Prone" is the strange word here, because it's an adjective but you tried to use it as a verb. So someone IS prone (to something). It still sounds a little strange, perhaps a better word would be "open" or "susceptible".

it would be more easy to understand what people say in that country