If you have applied to work or reside permanently in the United States you will need to get a legal document translation for all important documents relevant to you and your family which are not in English. A legal document translation is not quite the same as a translation of restaurant menu. The translator must have a thorough knowledge of the legal terminology used for the target language.
However, if you need to get your foreign passport, birth and marriage certificates as well as references from your past employees and your C.V. translated for immigration purposes you should ensure you hire a legal document translation expert who fully understands the terms in both languages of the documents requiring a translation. If you fail to do this and an immigration official representing the U.S.C.I.S. discovers part of or all of a document has been mistranslated then your application to work or live in the United States may be denied.
The U.S.C.I.S. does not require you get a legal document translation expert approved by them but the translation company you hire must be able to provide a written and signed statement stating that the translation is to the best of his or her knowledge accurate. It is actually a lot simpler than many countries who only allow a person who has been formally approved and who possesses certain translation qualifications to undertake the translation of legal documents for immigration purposes.