Why does it mention Kesav regarding Medinos, and Lashon regarding Amim?
Vilna Gaon: Four matters distinguish Umos - Kesav (how they write the letters), language, [its native] land, and dress. Sancheriv mixed up the nations; he settled people from this Medinah in another Medinah. The Kesav is according to the Medinah, but the nation continues to speak its language. Regarding the Medinah, he wrote to the Sarim; Sancheriv did not exile them. For the Am, he needed to write like the language of the current residents 1 .
Vilna Gaon (here and Divrei ha'Yamim I, 1:4): This answer's Ibn Ezra's question (Bereishis 27:40). The Targum of "v'Tzim mi'Yad Kitim" (Bamidbar 24:24) is v'Siy'an Yitztarhan me'Roma'ei. Kitim are from Yavan ("u'Vnei Yavan? Kitim" (Bereishis 10:4. This shows that Romi is not Edom!) Really, Sancheriv exiled Edom to Romi.
What is the significance of "that each man will rule in his house"?
Torah Temimah citing Megilah 12b: If not for the first letters 1 (which established the king to be a fool), there would not have remained any remnant of (the haters of) Yisrael (people would have rushed to carry out Haman's letters immediately, before the designated day). People said that the first letters are unnecessary, for even a bald man is the officer in his house!
Malbim: Until now, the etiquette in Paras was that a wife honors her husband. Now, he rules over her, like over a slave. He can deal with her like his property. So it is today in some places on Africa.
The text of Ya'aros Devash (2, Drush 9) and Malbim was 'if not for the first letters, the latter letters would not have been fulfilled.' Malbim - i.e. had the first letters not established that the king alone rules over laws and etiquette, the advisors would not have consented.
What is the Chidush that a man will speak his nation's language?
Rashi: If his wife speaks another language, he can force her to learn his language.
Malbim: Until now, all nations under Paras' rule, whatever they wrote to the king, and what the king wrote to them, needed to be in Persian, like the king's nation. All of them needed to learn Persian. Achashverosh solidified his rule. He, and not his nation, rules over the others. Paras is no different than any other Medinah under his rule. All are his slaves. There is no reason to favor Persian. The kingdom is not called on Paras, rather, on Achashverosh.
