Every local public agency, as defined in Section 54951, serving a substantial number of non-English-speaking people, shall employ a sufficient number of qualified bilingual persons in public contact positions or as interpreters to assist those in such positions, to ensure provision of information and services in the language of the non-English-speaking person. The determination of what constitutes a substantial number of non-English-speak ing people and a sufficient number of qualified bilingual persons shall be made by the local agency.