How will Mo'av resemble Sedom?
Rashi: Also you will return to your initial place - was your father Lot not from Sedom?!
Radak: It will be permanently destroyed.
Why will Bnei Amon be like Amorah?
Malbim: It was destroyed worse than Sedom. Lot and his two daughters were saved from Sedom [but no one from Amorah survived].
What is the meaning of "mi'Mshak Charul"?
Rashi: This is thorns making noise, like "k'Mashak Gevim" (Yehoshua 33:4). Also the first Mem is from the root, like "Mimshach ha'Sochech" (Yechezkel 28:14). Thorns will grow there, for no one passes by. They bang each other, and make noise 1 .
Radak #1, Malbim: It is a place from which thorns come out, like a ruin.
Radak citing his father: This is abandoning. The land will be abandoned to thorns. This is like Targum Yonasan Mishmat Meluchin. Meluchin is like "Malu'ach Alei Si'ach" (Iyov 30:4), thorns.
Radak #2: This is like "u'Ven Meshek Beisi" (Bereishis 15:2), from the root Shuk. There, Radak explained that it is going back and forth.
What is "Michre Melach"?
Rashi: A place where they dig (mine) salt. Radak #1 - this is like "Ki Yichreh Ish Bor" (Shemos 21:33). The Targum here is u'Machafurin di'Mlach. Malbim - there is "Gafris va'Melach Sereifah Chol Artzah" (Devarim 29:22) in Arei ha'Kikar.
Radak #2: It is a mound of salt. Michre is like Kri. One who begins measuring [his stack], he says 'Baruch is the One who sends a Brachah in this Kri' (Bava Metzi'a 42a).
Why does it add "v'Yeser Goyi Yinchalum"?
Radak #1: This repeats "She'eris Ami 1 Yevazum." Perhaps this was in Bayis Sheni, when they returned from Galus Bavel.
Radak #2: This will be in the future, in the days of Mashi'ach. "Ki Razah Es Kol Elokei ha'Aretz" (11) supports this.
Radak: There should be another Yud at the end of Goyi, for the pronoun (My Goy). It is omitted, but the vowel (Chirik) is pronounced.