How you speak your language can be the determining factor which associated the way you are. The ideas of Sociolinguistics played a huge part in this movie, so I want to provide my thoughts on the idiolect and dialects parts in My Fair Lady. I divide my thoughts into two parts (dialects and idea of idiolect.)
Dialects show where the people were from. Different dialects helped professor Henry Higgins distinguish the different people, and give the brief identification of the social classes, economy situations, and life styles. He knew the upper-classed man had had been to India, where the father of the flower seller originally came from, and Eliza Doolittle was a good example for his sociolinguistics study.
Idea of idiolect can tell who the people are, and how the people speak their native language was stock on them. It will be hard to change it when they are old enough. The idea of idiolect even let professor Henry Higgins mad about Eliza Doolittle. He had an idea that if this lady could have spoken her native language well, she could go up to the upper class. This idea in the end came true. Eliza Doolittle went to the ballroom after she changed the way she spoke, and every upper-classed member died to know which rich house she came from. Eliza Doolittle took a long mile to learn how to enunciate properly, and the changing let her have more opportunities to get a better job, knowing more people, and learning more about herself.
How people speak their native languages and the ways they talk can be the methods for us to know they better. The two factors are not unchangeable and the changing of those helps us know the people better.