A. Yusuf Ali:Translation:
At length when he had furnished them forth with
provisions (suitable) for them, he put the drinking cup
into his brother´s saddle-bag. Then shouted out a
crier: "O you (in) the caravan! behold! you are thieves,
without doubt!" 1737

Muhammad Asad:Translation:
And [later,] when he had provided them with their provisions, he placed the [King's] drinking-cup in his brother's camel-pack. And [as they were leaving the city,] a herald 71 called out: "O you people of the caravan! Verily, you are thieves! 72
1737 Joseph's plan was to play a practical joke on them, which would achieve two objects. Immediately it would put them into some consternation, but nothing comparable to what he had suffered at their hands. When the plan was unravelled, it would make them thoroughly ashamed of themselves, and dramatically bring home their guilt to them. Secondly, it would give him an excuse to detain Benjamin and bring their aged father into Egypt . He contrived that a valuable drinking cup should be concealed in Benjamin's saddlebag. When it was found after an ostentatious search, he would detain the supposed culprit, and attain his object, as the story relates further on.