What is the role of language in cultural development?

A rather broad question isn't it? This calls for a broad answer. Language's role is chiefly to facilitate communication and to make specific and detailed thought possible. It's role in cultural development is no different from its role altogether. If you want more detailed information about language and its role in the development of specific cultures, you're not likely to get any here, as this is a very widely discussed subject which is quite possibly much disputed and on which there is already a great deal written.