Aside from Spanish to English translations of birth certificates, I love translating affidavits. An affidavit (also called a declaration or personal declaration by some immigration attorneys) is a statement of fact that a person writes down and then signs under oath and under penalty of perjury. Given the serious nature of these documents, having an exact Spanish English translation is very important!
Affidavits can vary in length from a single page to twenty or more pages (I have translated both!). They are generally drafted by an attorney after interviewing a client. Attorneys then normally ask their clients about the facts in the affidavit to make sure everything is correct, and then they ask the client to sign. True affidavits (as opposed to declarations) often require a notary public signature and seal.
As an experienced Spanish to English and English to Spanish legal translator, I have translated affidavits for asylum and U visa cases, family court matters, and criminal defense attorneys and clients.