Will declaring our city an Official Multilingual City undermine English as our common language?

No. Multilingualism is about mastery of two or more languages. English is the common language of the United States. Everyone needs to have the opportunities to develop full literacy in English, and an official multilingual city is one that supports the development and use of English as one of the languages. It also supports the development and use of languages other than English. There are great benefits for individuals who know more than one language, and tremendous benefits to a city to foster those skills. The more languages a person knows, the deeper their understanding of and mastery of literacy overall. Literacy in languages other than English strengthens mastery of English.