Saw this movie onthe TV, 70’s to early 80’s.  I do not know the cast, but the plot was about a son of a diplomat became a courier.  Some of his skills were the ability to speak 18 languages, some fighting skills, extremely intelligent.  He was assigned to clandestinely escort a woman to testify to some court.  She had a letter she carried and a tracking device was hidden behind the stamp on the letter.  They slipped away from the bad guys by hiding the tracking device on a biker.