What if the signer doesn't speak English? The notary must be able to communicate directly with the signer. If the notary knows enough of the signer's language to communicate, then its okay to notarize that person.
Don't allow an interpreter to help you communicate with the signer. The signer's daughter or son may assist as a matter of habit. Don't allow this.
If someone offers you a job over the phone, and you get the impression that not everyone in their family speaks English. Ask, who the signer is, and if they speak English.