Combining 母 (mǔ) and 语 (yǔ) gives you 母语 (mǔyǔ), a direct and clear compound word meaning “mother's language” or “mother tongue.”
In many Western countries, the concept of a “mother tongue” is fairly simple; it's the primary language of the country you grew up in (e.g., English in the USA, French in France). In China, the concept of 母语 is more layered and fascinating. The key distinction is between 普通话 (Pǔtōnghuà), the official national language (Mandarin), and the hundreds of 方言 (fāngyán), or local dialects. For tens of millions of Chinese people, especially those from regions like Shanghai, Guangdong (Canton), or Sichuan, their true 母语—the language they spoke first and use with family—is their local dialect (e.g., Shanghainese, Cantonese). They learn Mandarin in school as a second, official language. Therefore, a person's 母语 is deeply tied to their regional identity and heritage. It represents a connection to one's hometown, local culture, and history, which often stands in contrast to the unifying, official identity represented by Mandarin. Asking someone from Guangzhou “你的母语是什么？” (Nǐ de mǔyǔ shì shénme?) might elicit the answer “Cantonese,” not “Mandarin,” highlighting a strong sense of local pride. This is different from the US, where answering “What's your mother tongue?” with “a Boston accent” wouldn't make sense; the underlying language is still English. In China, the dialect can be mutually unintelligible with Mandarin, making it a distinct language in practice, and thus, a distinct 母语.
母语 (mǔyǔ) is a common term used in both formal and informal settings.
The connotation is generally neutral and descriptive, but when used in the context of dialect preservation, it can carry a strong emotional weight tied to cultural identity.