Do you know how stressful it is being questioned? I was waiting to pick someone up from a train station in Spain when security approached to tell me the station had closed, and why was I still there. All the Spanish went out my head. I imagine being questioned by congressional investigators is probably even more stressful.
I was once on a jury in California in a case where several witnesses gave testimony through a Spanish interpreter. It seemed clear that some of the witnesses who testified through the interpreter were fluent in English, and so it seemed a little gratuitous to me at the time. Later on I understood that it made sense both for reducing the stress in the situation and for avoiding any minor linguistic misunderstandings in cross-examination that a lawyer might try to make a big deal out of. It's quite possible that the lawyers encouraged their witnesses to use the interpreter.
It sounds like a bad idea all around.
I'm more concerned that the persecution, understanding how stressful the situation is for me and how not being a native speaker I wouldn't necessarily be familiar with legalese or very formal lexicon, uses it against me to extract a confession due to my confusion, than I am that the nuances would be lost through an interpreter.
I speak English with the police, even for trivial things where I'm the one requesting service, like when I lost my wallet. That is not a context where I want to get anything wrong, and where there is absolutely nothing to be gained from showing off what I learned in language class.
Though to be fair, the Sammy Sosa anecdote was more for humor than anything else. Oddly it turned into a comment that got 50 upvotes.
I appreciate the response, I think you've flipped my thinking on this:)