You don't need to understand all the word to understand a song. With Geoirges Brassens, for example, I believe there are plenty of French people who don't understand all the words and the idioms he uses.

Often enough with a song it can be years after I've been enjoying hearing it, before I actually make sense of the details of what is being sung, and that can apply just as much in English as in a foreigh language.

If we turn a deaf ear to people singing in laguages we don't understand, we turn a deaf ear to most of the music of the human race. We should never fool ourselves that any translation can ever tell us the whole story and give us the whole picture.

Sometimes a translation can be a great song in itself ("The Dove"). More often it can give us the key to making sense of the original. Very rarely indeed can it do both things at the same time. Translating songs is hellishly difficult, and as Rod McKuen demonstrated in the case of Jacques Brel (eg "Seasons in the Sun", "If you go away"), it is all too easy to make a complete Cod's arse of it.