Many people add languages after childhood. A second language is any language learned after the first language is already established, whether through formal instruction, immersion, or both.

Second-language acquisition research studies age effects, transfer from the first language, motivation, and instructional methods. Outcomes range from basic conversation to near-native proficiency. Accent and subtle grammar often remain challenging for late learners.

Second languages serve education, migration, trade, and identity goals. Policy decisions about when and how to teach them shape national linguistic repertoires. The term is conventional; some learners acquire third or fourth languages under similar conditions.

• Language learned after the first language
• Acquired through instruction, immersion, or both
• Subject of second-language acquisition research
• Serves practical and identity-related purposes