A lifetime of speaking two or more languages appears to pay off in old age, with recent research showing the symptoms of dementia can be delayed by an average of four years in bilingual people.

Multilingualism doesn't delay the onset of dementia—the brains of people who speak multiple languages still show physical signs of deterioration—but the process of speaking two or more languages appears to enable people to develop skills to better cope with the early symptoms of memory-robbing diseases, including Alzheimer's.

Scientists...