Language diversity can indicate a growing bilingual or multilingual population, and it may also indicate a need for language instruction or bilingual services and communication.

In 2017-21, 33% of Brookline residents spoke a language other than English at home, up slightly from 29% in 2000. This is higher than the state rate of 24%, which increased 5 percentage points since 2000, and higher than the national rate of 22%, up 4 points.

Everett had a much higher percentage of people who speak a language other than English than Brookline at 62%. Cambridge was similar to Brookline at 35%, while both Newton and Arlington have smaller percentages at 25% and 22% respectively. All localities experienced a growth of 3-5 percentage points since 2000, with the exception of Everett which saw an increase of 32 points.

The multiyear figures are from the Census Bureau's American Community Survey. The bureau combined 5 years of responses to the survey to provide estimates for smaller geographic areas and increase the precision of its estimates. However, because the information came from a survey, the samples responding to the survey were not always large enough to produce reliable results, especially in small geographic areas. CGR has noted on data tables the estimates with relatively large margins of error. Estimates with three asterisks have the largest margins, plus or minus 50% or more of the estimate. Two asterisks mean plus or minus 35%-50%, and one asterisk means plus or minus 20%-35%. For all estimates, the confidence level is 90%, meaning there is 90% probability the true value (if the whole population were surveyed) would be within the margin of error (or confidence interval). The survey provides data on characteristics of the population that used to be collected only during the decennial census. Data for this indicator are released annually in December.