Yoseif knew all 70 languages (including Egyptian) plus Hebrew. This comes up in a Medrash explaining what Yoseif had over Pharoah.

Should we presume that the brothers also knew all these languages?

Why then in Yoseif's case of speaking with Pharoah (and other Egyptian officials before that) did Yoseif speak in a language Phahaoah understood, presumably Egyptian; yet the brothers spoke through Yoseif's interpreter, presumably speaking in Hebrew?

Furthermore, what was the purpose in speaking through a translator? If only Yoseif knew that Pharoah did in fact not know Hebrew, would there have been a problem if Yoseif, as Egyptian Overseer, knew how to speak Hebrew?

Perhaps if Yoseif did speak directly to the brothers in Hebrew it would have given away his real Jewish identity to them? But through an interpreter, he could speak more softly and without their connecting too closely with nonverbal communication? And it would not have given the brothers the freedom to speak about their guilty feelings among themselves if they knew Yoseif understood.

As a follow-up, Midrash on the subsequent parsha when Yoseif asks all the Egyptians to leave while he reveals his true identity to his brothers...

Surely he spoke to them in Hebrew?

How did the Egyptians figure out what was said?