Here's a PDF from the IATA that lists most of the tax codes:
http://www1.iata.org/WHIP/_Files/WgI...ax%20Codes.pdf

The ones of yours I know off the top of my head are UB for UK PSCs, AY is a US segment tax, XY, YC, and XA are US customs and immigration, XF is US PFCs. XT is a catch-all code where multiple fees are combined into one line. DE I would guess is a German fee of some sort.