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 2016-20, 24% of MetroWest residents spoke a language other than English at home, up from 18% in 2000. This is on par with the state rate (24%), which increased 5 percentage points since 2000, and slightly higher than the national rate (22%), up 4 points.

Framingham, at 38%, has the most language diversity, followed by Lexington at 36%, and Waltham and Marlborough, both at 33%. The four localities' rates increased by 9, 17, 6 and 14 points, respectively, since 2000.

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.