I'm not sure how official it has to be. I know that for other documents USCIS gave a sample:
TO WHOM IT MAY CONCERN:
I, ______, certify that I am competent to translate from (language) To English and that the translations of the following document _________is a correct and true translation to the best of my knowledge and belief.
Signed,
______Date:______
I think anyone can translate and sign a statement like that, but not sure. Hopefully someone with experience will reply!
My husband's certificates, though issued in small villages, were surprisingly both in English and Telugu, so we didn't have to translate anything.