Here is a list of the approved seats on Lufthansa. I know that they also accept non-German seats that are airline approved (such as FAA approved seats, done that!)
I couldn't find on their site whether the seat has to be forward-facing but on the list, there are a number of infant bucket-style seats which only install rear-facing, therefore, it must be allowed!
http://www.lufthansa.com/mediapool/p...systems%20(PDF)