Allahpundit has a fairly good discussion of some of the practical difficulties involved in this decision, which actually says that the New Mexico State constitution requires courts to seat jurors who do not speak Engliah.
But what leapt to my mind were the difficulties that might arise in a highly diverse area like Los Angeles. You could have a jury pool where one juror speaks Spanish, another speaks Mandarin, a third speaks Cambodian, a fourth speaks Japanese, and the other eight speak English.
A witness might be giving testimony in Spanish, translated by a court interpreter into English, translated into the above languages by the above interpreters. (Yes, the Spanish would probably have to be translated back into Spanish. Court is weird that way.) You’d have about six people talking in close proximity. It would be a wonder if anyone could hear anything.
And wouldn’t those jury deliberations be fun? Imagine the confusion as one juror makes a comment in Cambodian, it is translated into English, and then translated back into three other languages.
All nuance would be lost, discussion would be a game of telephone, rife with misunderstanding, and it would generally be a disaster.
I can see why defendants would like it. (Confusion and chaos tend to favor the defense.) But why any sensible person would willingly choose such a regime is beyond me.
Some civic duties, if not all, are best conducted by citizens able to speak a single common language. Jury duty is one of them.