Extract of the terms & conditions:
The voucher can be redeemed between 16/05/2012 and 31/05/2012.
Travel must be between 03/06/2012 and 31/12/2012.
Vouchers are only valid for itineraries where all flights are operated by Lufthansa and Lufthansa Regional Partner (incl. Lufthansa City Line and Eurowings).
The voucher is only valid for flights departing in Germany.
Link:
https://promotion.lufthansa.com/pl_amarketing/?lid=en
https://promotion.lufthansa.com/pl_amarketing/?lid=de