This shifts from the main story line to background information that explains why the brothers thought Joseph could not understand them. (See: [[rc://en/ta/man/translate/writing-background]])
An "interpreter" is someone who translates what one person says into another language. Joseph placed an interpreter between himself and his brothers to make it seem like he did not speak their language.
Here the people are represented by their "eyes" to emphasize what they see. AT: "bound him in their sight" or "bound him as they watched" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
This can be stated in active form. AT: "The servants did for them everything that Joseph commanded" (See: [[rc://en/ta/man/translate/figs-activepassive]])