As I said, the representative of Beosport (Wilson & Luxilon authorized distributor in Serbia) was very professional in the email correspondence and provided me details of the origin of the imported goods (Amer Sport Munich, Germany). He said that he was looking in German price list in front of him and that all strings are quoted as "Made in Belgium". He was not sure about bar codes, as he never thought about that before, but promised to inquiry German partner.
He invited me to call him by phone or visit him if I have any addition questions. Although this is not a "hard evidence of authenticity", it leaves me assured that they are serious company that would not bet with their reputation and country distributor status.
The other individual who is extremely well informed on all Luxilon products, also did take a look at the macro-photos and bar codes and confirmed that they look absolutely authentic. For me, this is good enough