as to Du translating as 'thee'...perhaps that is so, but in the US, 'thee' & 'thou' are primarily associated with the older Quaker form of address, and don't quite convey the German sense of close acquaintance as opposed to casual acquaintance, if I understand it correctly, so it would still be slightly 'curious' in a song if the form changed from 'you' to 'thee' for an American.