Calpurnia speaks two languages - 'white folks' talk' when she is with the Finches or among white people and the Negro dialect when she is among coloured people. Calpurnia has learned to roll with the punches to belong to both worlds. In this respect she is like a bridge joining the chasm between the two cultures. She is decades ahead of her time in adaptation and integration.
An observation: Calpurnia is much like Dolphus Raymond in that she offers the community what they expect from her to have some peace of mind. Calpurnia "talks nigger" and "white" alternately to be a part of both cultures; Dolphus Raymond pretends to be an alcoholic to "justify" his alternative lifestyle and his preference for black people.