For anyone who hasn’t thought about translation issues recently, go read John’s post about it, including the comments. I wish I had something useful to add, but it seems to me the ground has been covered pretty thoroughly.
Every time I think about this issue I come to a slightly different conclusion. I love being able to understand both music and text – my enjoyment of Lieder recitals would not be nearly what it is if I didn’t have access to translations of the texts – but I’ve noticed that when I am most enjoying opera or song, I am not hearing words. I’m probably noticing them on some level, but I don’t have the feeling of listening to them or even being aware of them. (But to split a hair even finer, not hearing English in this way is for me, an English-speaker, different from not hearing German or Italian.) And as one of the commenters to the above-linked post pointed out, it’s nice to have super/sub-titles especially when you understand a bit of the language of the opera, because they can jog you just enough that you parse what the sung text means in a quicker way than if you had to stop and think about it without a translation.
I suppose the only other thing I would say about the translation/original language issue is that when I think about this, my impulse is to ask what kind of experience opera should be, and then whether/how translation gets people there. And of course there are almost as many answers to the “what should listening to opera be like” question as there are opera-listeners.