I am looking for information on interpreter requirements. For example Mom has an individual dda. Mom does not speak English. Her 'daughter' who is not on the account is contacting us on Mom's behalf. We not want to create a discrimination issue but also need to protect our account holders information. Any guidance will be appreciated!

Not sure where you are going to find any guidance. If the mother wants the daughter to act on her behalf, they should get a POA or do this in person with Mom present.