Maggie's right about how hard interpreting is - I've done it too and it makes me exhausted, sick and with a raging headache - no matter what the subject matter might be.
As for simultaneous translations - this is the stuff of nervous breakdowns, especially when doing German to English, as you have to hold a huge string of words in your head while waiting for the verb, which comes at the end of the clause in German and the beginning in English! All this while listening to the next sentence. I've trained in it but never done it, not being a masochist.
The point I'm trying to make is that everything about a second language is complex, and can be a nightmare. Many people can't do it, others can only manage a little, and many who speak two languages fine, cannot translate or interpret. Immigrants who don't speak English are rarely willfully refusing to do it. We are simply asking too much of them. Luckily the children, pre-puberty, just absorb the prevailing language, like osmosis.