According to the USCIS General Tips on Assembling Applications for Mailing, documents not in English must be accompanied by an English translation. The translator must certify that s/he is competent to translate and that the translation is accurate. Translations do not need to be done by a professional; a friend or family member can be the translator as long as s/he is competent to translate. It is highly recommended that you do not translate your own documents.
The format of the translation should include the translator's name, signature, address, and date of certification. A suggested format is:
CERTIFICATION BY TRANSLATOR
I
[typed name], certify that I am
[fluent or conversant] in the English and
[enter appropriate language] languages, and that the
[above or attached] document is an accurate translation of the document attached entitled
[enter title of document].
Signature: _____________________________________________________
Typed Name: __________________________________________________
Address: _______________________________________________________
Date: __________________________________________________________
Additional Resources:
UW-Madison Cultural Linguistic Services
A quick web search for "Translation Services" will give you a list of many professional translation services