If you are not fluent or comfortable in English, and need to attend an interview at an office of U.S. Citizenship and Immigration Services, in particular a green card (adjustment of status) interview, you might need to bring your own interpreter. That way, the USCIS officer and you can communicate through this person acting as intermediary.
Exceptions to this broad rule include removal (deportation) hearings, at which an interpreter will be provided by the U.S. government, and naturalization (citizenship) interviews, because you are expected to know and be tested on your English language ability unless you've applied for a waiver based on age or disability.
Here's what to know before you ask someone to serve as your interpreter at a green card interview at USCIS.
The standards for interpreters (sometimes called translators, though technically translators handle only written text) who assist at interviews at USCIS field offices are set forth in a Policy Memorandum that USCIS issued on January 17, 2017. This guidance does not cover situations where USCIS itself provides the interpreter; nor does it cover asylum, NACARA, credible fear/reasonable fear, naturalization, or overseas interviews.
The interpreter you bring to your interview must be someone who can accurately, literally, and fully interpret for both you and the interviewing officer and be able to interpret impartially and without bias.
Certain people are not eligible to serve as interpreters at all, namely minors under the age of 18 (though an exception for good cause, such as lack of local interpreters who speak that language, may be made if the person is at least 14), witnesses in the case under consideration, and the applicant/interviewee's attorneys and legal representatives.
The guidelines also give USCIS the power to disqualify someone from serving as interpreter, if the person is not sufficiently fluent in both English and in the interviewee's language and able to interpret competently, impartially, and without bias. This means that, for example, a family member with a personal interest in the outcome of the case might not be allowed to serve as interpreter. In fact, USCIS explicitly says within its guidelines that "family members will generally be disfavored as interpreters if there is another qualified interpreter available to the customer."
Fortunately, you need not necessarily pay a professional. The USCIS policy memo says nothing about any sort of objective qualification, only that the person must be able to do the job.
So it's possible that you can find an adult friend (not a family member or your lawyer) who is capable of handling this role. If not, talk to local nonprofits serving immigrants or search online to hire someone.
The two of you should, if possible, practice beforehand. It's not easy to get into the rhythm of having someone interpret for you. You'll need to speak relatively slowly, and stop every few sentences, in order to give the interpreter the chance to fully hear and then repeat your words in English without forgetting what you said. And, practice gives your interpreter a chance to get used to your pronunciation and so forth.
The interpreter and you will have to jointly submit Form G-1256, Declaration for Interpreted USCIS Interview. Both the interviewee and the interpreter will be asked to sign this form at the start of the USCIS interview.
The form declaration states that the interpreter must accurately, literally and fully interpret for both the interviewee and the interviewing officer. It also reminds the interviewee that an interpreter might hear personal information, and requires the interpreter to agree not to disclose any such information learned in the interview.