If you are interested in these promotional flights with Air China please look for flights in travel period between 1st of November 2014 till 31st of March 2015. (except blackout period during Christmas holidays).
Booking samples - for more deals based on Air China please refer to this article
Barcelona - Bangkok - Frankfurt for €357
Barcelona - Bangkok - London for Ł324
Stockholm - Chiang Mai and Bangkok - Germany for €406
Stockholm - Chiang Mai and Bangkok - London for Ł354
Stockholm - Chiang Mai and Phuket - Germany for €484
Stockholm - Chiang Mai and Phuket - London for Ł354
Stop-over in China is also available for additional fee. To check your connection possibilities we recommend to use service of Skyscanner. This tool gives you quickly an idea which airlines are available from your homecity. To check some affordable accomodation you may use service of booking servers such as Hotels.com or Hotelopia.
Booking sample of cheap flights to Thailand during main tourist season 2014/2015 for €358 here. In this case you would be flying from Barcelona to Bangkok on 1st of February. Your return flight from Asia back to Germany would be on 14th of February 2015.