Lufthansa’s discount voucher of the ‘Muttertag’ and ‘Vatertag’ Promotion is still vaild untill 27 July. Lufthansa has a separate page for these 20€ voucher codes here.
The basic T&Cs are:
- Only for flights departing from Germany
- Book between 2016-04-23 and 2016-07-23
- Travel between 2016-04-32 and 2016-10-23
- Limited to 1 code per mail address
If you get an error stating “no more vouchers available” try again the following day. It seems as if there is a daily limit.