The term "mother tongue" means "native language." Tan's title is a play on words which makes the point that her own mother tongue is not the same as that of her mother, a native speaker of Chinese. The author reluctantly describes her mother's English as "broken," in contrast to her own polished use of English, not only as a native speaker, but as a professional writer who relies on her own command of language for her livelihood and sense of identity.

When she was growing up, and even after she became a writer, Tan was embarrassed by her mother's limited command of English. However, she often used and continues to use this style of English in her private life, even when talking to her husband, a native English speaker. It took her some time to realize that the formal English she learned in school was not always superior to her mother's way of speaking. When she wrote the first drafts of The Joy Luck Club, she found herself writing sentences such as "That was my mental quandary in its nascent state." Such pretentious language, she realized, is nobody's mother tongue. It also seemed wrong to be writing stories about Chinese mothers which her own Chinese mother would not be able to understand.

Tan is a writer whose major themes include her Chinese-American identity and the relationships between mothers and daughters. It was therefore an important step in her development as a writer when she embraced her mother's way of speaking English as a colorful, pithy alternative to the more formal language she had hitherto used exclusively. Her mother's use of language is now an important part of her writing, as well as her identity.