It has been in the news lately that the President has had a number of private head ups with Putin. On the news someone suggested (Don't remember if it was a congress person or the newscaster), that the Interpreter should be subpoenaed to testify about what was said.
One of the basic ethics for Interpreters is confidentiality of a conversation between two people. It does not seem that this confidentiality is *codified in the USA, the ethics being defined by associations.
*Some courts have rules and guidelines and a few states have laws dealing with court room Interpreters.
At any rate it does not seem that Interpreters have any kind of privilege like lawyers and other professions have to varying degree with clients. I would imagine that is because criminals don't use professional Interpreters very often and the issues surrounding any privilege for an Interpreter have never come up with much if any frequency.
Can Congress compel the interpreter to testify, or can The President stop such testimony?
Added: How about we take it out of the presidential realm, might actually be a bad example I used. Maybe say it was a translated conversation between diplomats or cabinet officers, and for whatever reason (not necessarily malicious), the person just doesn't want to answer any questions about the conversation or they became incapacitated, got pissed and quit the job, or died. So the interpreter is called as a witness. Can the interpreter be compelled to testify under subpoena from Congress? How about not under subpoena but something like the Ambassador has died what did they talk about when they last met?