How can Chinese have a common written language but different spoken languages?

Isn't it true that the purpose of writing was to be able reproduce spoken words? In Chinese languages even if the writing is not capable of reproducing common sounds, it is capable of communicating the same meaning. If the oral language preceded the written language, as we all think, then how can it be explained that a written language was agreed by people who speak differently?

Does china accept french as the international language of diplomacy or use English and Chinese languages ?

Does china accept french as the international languge of diplomacy or do they use english and chinese languages for thier official foriegn affairs discussions ?

How can i learn the chinese languages mandarin & cantonese ?

How can I learn the chinese languages mandarin & cantonese ? I don't have any money to go into an extra class in my school or to take classes outside of school, how can I learn these languages ? There is an chinese girl in school who i want to date so i want to learn chinese to talk to her.

How can Chinese have a common written language but different spoken languages?

Isn't it true that the purpose of writing was to be able reproduce spoken words? In Chinese languages even if the writing is not capable of reproducing common sounds, it is capable of communicating the same meaning. If the oral language preceded the written language, as we all think, then how can it be explained that a written language was agreed by people who speak differently?