Yes you interpret it, as it is described and presented (in lay terms) by both the defense and prosecution, as filtered by an impartial judge.
And incompetent representation is grounds for an appeal. I'm not sure what exactly that has to do with the fact that John Doe off the street is probably not equipped to read primary source material on legal precedent and interpret it correct on his own.
In the end, won't the jury have to interpret "case law"? How can you be presented something without interpreting it.