וְהִנֵּ֤ה עֵֽינֵיכֶם֙ רֹא֔וֹת וְעֵינֵ֖י אָחִ֣י בִנְיָמִ֑ין כִּי־פִ֖י הַֽמְדַבֵּ֥ר אֲלֵיכֶֽם׃
Or, vous voyez de vos yeux, comme aussi mon frère Benjamin, que c’est bien moi qui vous parle.
Siftei Chakhamim
In the sacred Hebrew tongue. Because it is written here, “And speak to the people,” and elsewhere in parshas Vayishma Yisro (Shmos 19:19) it is written, “Moshe spoke and Hashem responded with [His] voice.” Just as there it was in the sacred Hebrew tongue, i.e., the Ten Commandments, so too, “and speak to the people” is in the sacred Hebrew tongue (Sotah ibid). Alternatively, it is written regarding Yosef (Bereishis 45:12), “That I speak to you with my own mouth.” Just as there it was in the sacred Hebrew tongue, so here too it is in the sacred Hebrew tongue.
Siftei Chakhamim
Not to reveal about the Hebrew Language... Question: If so, how was Yoseif allowed to speak to his brothers in Hebrew? Rashi explained [that Yoseif spoke to them in Hebrew] on, “I speak to you with my own mouth” (45:12). The answer is: Pharaoh stipulated with Yoseif not to speak Hebrew specifically to the Egyptians. When Yoseif spoke to his brothers, no one else was with him in the house, and it did not become known that he spoke to them. (Re’m) The Nachalas Yaakov writes: The real question is that everything Yoseif’s interpreter spoke [to the brothers] was in Hebrew, and many Egyptians were present. Furthermore, Re’m contradicts himself, because he wrote on 45:12 that many Egyptians knew Hebrew [since it was the language of the neighboring land of Canaan]. If so, what use was it for Yoseif to swear not to speak in Hebrew, when many Egyptians were speaking it [even though Pharaoh did not understand Hebrew]? See his elaboration there.
Or HaChaim
וישלח את אחיו, He sent off his brothers, etc. This means that Joseph sent everybody home, including Benjamin. Benjamin's testimony would convince Jacob most of all; this is why Joseph had already stressed previously (45,12) that Benjamin was a witness that he was Joseph. Now that Yehudah had fulfilled the conditions of his guarantee it is clear that if his bones rattled in his coffin during the years Israel travelled in the desert this was only because he failed to have his vow annulled, as pointed out in Megillah 11.