"Journey to the Lost City" is not a specific film by Fritz Lang but the combination of Der Tiger von Eschnapur (1959) with its sequel Das indische Grabmal (1959), done in 1960 by American International Pictures.
The wife of the Swedish Ambassador of Greece becomes involved in a romantic triangle, but the man who comes between husband and wife has a preference for the husband.
Paul Hubsschmid is Paul Finney aka Upperseven, master of disguise. He's out to stop a diamond smuggling operation which fronts for a missile building project.
An out-of-work and penniless American pilot is offered work in Mozambique and promptly becomes an unwitting pawn in a world of drug smuggling, kidnap and murder.