Why does achebe use dialect in his story?

Achebe uses a certain dialect to portray how different Igbo culture was in comparison to to the Western world countries. Igbo culture was unique and by using their unique dialect, the reader would be able to interpret the story in a way that brings out Achebe's message best without altering the language to the extent that its value as a medium of international exchange will be lost. Achebe accomplishes this goal by innovatively introducing Ibgo language, proverbs, metaphors, speech rhythms and ideas into a novel written in English.

Sorry it's not much but... hope I helped :)