The language Kazuo Ishiguro uses in his novel is realistic and reflects the time in which the novel is set (the 1990s). Kathy and her friends speak very much as you would expect young people to speak, although at the same time it is impossible to deny that there is something rather middle class about the language they use and the context of their discussions,
I’d assumed Ruth was something of a chess expert and that she’d be able to teach me the game. After all, Hailsham is perceived as being a rather prestigious school to attend and until the reader knows differently, it could almost be seen as a private boarding school.
Kathy is a chatty and open narrator and her engaging style makes it easy for the reader to become absorbed in the novel. She does not clutter her narrative with difficult words, although she does make several literary references to novels she is reading and these help to reflect the realism of her education at Hailsham, "I was lying on a piece of old tarpaulin reading, as I say, Daniel Deronda..."
One of the key aspects of Kathy’s narration is that it uses the language of acceptance. Neither Kathy nor the other clones ever use words which reflect the fact that they might be tempted to rebel against their future roles as donors. They simply accept the fact that before they are middle aged they will have completed and that their lives will be over. Their language choices are not those of rebels who are planning a revolution but rather the language choices made by a class of people who have quietly accepted their future fate.
Kathy and her friends use a mixture of formal and informal language and can pick the right occasion to make the right language choices,
Don’t talk rubbish Tommy. (Kathy to Tommy)
Kazuo Ishiguro is making his novel as realistic as possible. Therefore the students know that they must speak in a more formal way when speaking to a guardian but when speaking to their friends, they are informal and relaxed.
This allows the reader to see that the clones are exactly the same as humans of the same age. The student clones behave and react in similar ways. Therefore, when society finds it acceptable to use the clones in order to donate their vital organs, the reader can see for themselves what a truly dystopian society this is.