Diffusion refers to the process by which an idea or object spreads from a place of origin to other places without the necessity of migration. Think of mass communications, for example. Acculturation refers to the process of migration in which two groups of people come into contact with each other. As a result of this contact, each group is affected by some degree of merging or adapting of features. Think of the European immigrants coming to the U.S. Assimilation is a form of migrational change wherein one group totally merges into another group and loses its original identity.
Assimilation is quite rare whereas acculturation is much more common.
Language can be defined as human symbolic communication. For geographers, language can be used to identify culture regions, to identify where a person comes from, to identify the diffusion route taken by people and their culture. The Ural-Altaic family is represented in Europe through the languages of Finland, Estonia and Hungary. The Afro-Asiatic family predominates in northern Africa and much of the Middle East, including the languages of Arabic and Hebrew. The Niger-Congo family predominates over most of SubSaharan Africa, including the Bantu languages.