There is a lot of misunderstanding about what the U.S. Government actually requires of translations of immigration documents. Some people think that the translator has to be "certified" but that is not true. In fact, the translator apparently does not even need to be "fluent" (whatever that means) in English and the foreign language.
Here is what the rules on the website of U.S. Citizenship and Immigration Services say:
Please submit certified translations for all foreign language documents. The translator must certify that s/he is competent to translate and that the translation is accurate.
The certification format should include the certifier's name, signature, address, and date of certification. A suggested format is:
Certification by Translator
I [typed name], certify that I am fluent (conversant) in the English and [enter appropriate language] languages, and that the above/attached document is an accurate translation of the document attached entitled [enter title of document].
Therefore, it appears to be sufficient for USCIS purposes if the translator is merely "conversant" in English and the foreign language and certifies that the translation is accurate. That is it. Nothing more is required.