In Govt. Contracting, is there a clause or some wording we can put in the PWS that would require workers/employees to be able to understand, speak and have a meaningful conversation in the 'common' language? Thank you.
The short answer to your question is, NO there aren't any clauses that specifically require all employees of a given contractor be able to speak the 'common' language, presumably English.
Title VII of the Civil Rights Act of 1964 are federal laws that protects individuals from discrimination based upon national origin and race. Some courts and government agencies have said that discrimination based on language is a form of national origin discrimination because primary language is closely related to the place a person comes from.
Language discrimination is the unfair treatment of an individual solely because of their native language or other characteristics of speech, such as accent, size of vocabulary, and syntax.
It appears that a course of action available to you might be for you to require that the supervisor be on site whenever work is being performed to address the potential safety issues, property damage, et al., but that likely would significantly increase the cost of the services.
The question of requiring all employees of a contractor to speak a 'common' language is not something that AAP can provide an answer for, since it would more appropriately be address by an attorney. It's recommended that you contact your local legal office for advice and direction with this issue.