linguistic:voice_change, structural:reformatting, quality:correction
Languages

English serves as California's de jure and de facto official language. According to the 2021 American Community Survey conducted by the United States Census Bureau, 56.08% (20,763,638) of California residents age 5 and older spoke only English at home, while 43.92% spoke another language at home. 60.35% of people who speak a language other than English at home are able to speak English "well" or "very well", with this figure varying significantly across the different linguistic groups. Like most U.S. states (32 out of 50), California law enshrines English as its official language, and has done so since the passage of Proposition 63 by California voters in 1986. Various government agencies do, and are often required to, furnish documents in the various languages needed to reach their intended audiences.

Spanish is the most commonly spoken language in California, behind English, spoken by 28.18% (10,434,308) of the population (in 2021). The Spanish language has been spoken in California since 1542 and is deeply intertwined with California's cultural landscape and history. Spanish was the official administrative language of California through the Spanish and Mexican eras, until 1848. Following the U.S. Conquest of California and the Treaty of Guadalupe-Hidalgo, the U.S. Government guaranteed the rights of Spanish-speaking Californians. The first Constitution of California was written in both languages at the Monterey Constitutional Convention of 1849 and protected the rights of Spanish speakers to use their language in government proceedings and mandating that all government documents be published in both English and Spanish.

Despite the initial recognition of Spanish by early American governments in California, the revised 1879 constitution stripped the rights of Spanish speakers and the official status of Spanish. The growth of the English-only movement by the mid-20th century led to the passage of 1986 California Proposition 63, which enshrined English as the only official language in California and ended Spanish language instruction in schools. 2016 California Proposition 58 reversed the prohibition on bilingual education, though there are still many barriers to the proliferation of Spanish bilingual education, including a shortage of teachers and lack of funding. The government of California has since made efforts to promote Spanish language access and bilingual education, as have private educational institutions in California. Many businesses in California promote the usage of Spanish by their employees, to better serve both California's Hispanic population and the larger Spanish-speaking world.

California has historically been one of the most linguistically diverse areas in the world, with more than 70 indigenous languages derived from 64 root languages in six language families. A survey conducted between 2007 and 2009 identified 23 different indigenous languages among California farmworkers. All of California's indigenous languages are endangered, although there are now efforts toward language revitalization. California has the highest concentration nationwide of Chinese, Vietnamese and Punjabi speakers.

As a result of the state's increasing diversity and migration from other areas across the country and around the globe, linguists began noticing a noteworthy set of emerging characteristics of spoken American English in California since the late 20th century. This variety, known as California English, has a vowel shift and several other phonological processes that are different from varieties of American English used in other regions of the United States.