Verse 20: This is the inheritance of the tribe of the children of Judah according to their families.
[This is the possession of the tribe of the sons of Judah] What had been said in verse 12 is repeated; because what things were narrated from that point to this concerning Caleb, Othniel, and Achsah, were spoken by way of digression and as a παρένθεσιν/parenthesis, for the very reason that they pertain to the distribution of the Jewish inheritance (Masius).
Verse 21: And the uttermost cities of the tribe of the children of Judah toward the coast of Edom southward were Kabzeel, and Eder, and Jagur…
[And the cities from the uttermost parts of the children of Judah were, etc.] You could translate it, partly of the children of Judah: for they were partly of Simeon, Joshua 19:1-9 (Grotius). The more famous cities at that time are not enumerated one by one, not indeed, as it appears, all in order, but nevertheless a great number (Masius). Not all: for omitted are two satrapies of the Philistines, Gath and Askelon; likewise three sacerdotal cities, Joshua 21:14-16; and also Bethlehem, or Ephratah, concerning which Genesis 35:16; Judges 19. Moreoever, other cities built afterwards were not, of which it is not treated here, but of those that belonged to the Canaanites before the coming of the Israelites (Bonfrerius). Joshua only enumerated cities on the borders and limits of Judah, not midland cities (Munster). Now, the great number of cities is a certain indication of the fecundity of the Promised Land. We will not persist in describing the individual cities; both because the situation and condition of many is not greatly conducive to a correct perception of the Sacred Histories, and also because they are little known to us. Now, the beginning of the Catalogue is made almost from that place from which also the Catalogue of borders began, that is, from the farthest shore of the Dead Sea westward, where Canaan shares a border with Idumea. And thence it proceeds almost to Gaza and the Mediterranean Sea (Masius).
The uttermost cities; those which were on the borders of the land, not the midland cities. It is apparent that all the cities belonging to this tribe are not mentioned in this catalogue. Kabzeel, called Jekabzeel, Nehemiah 11:25.
Verse 22: And Kinah, and Dimonah, and Adadah…
[Adadah] Hebrew, עַדְעָדָה; Septuagint, Gadgada. For they are generally wont to represent ע/Ayin by their γ/Gamma/g (Masius).
 Hebrew: זֹ֗את נַחֲלַ֛ת מַטֵּ֥ה בְנֵי־יְהוּדָ֖ה לְמִשְׁפְּחֹתָֽם׃
 Hebrew: וַיִּֽהְי֣וּ הֶעָרִ֗ים מִקְצֵה֙ לְמַטֵּ֣ה בְנֵֽי־יְהוּדָ֔ה אֶל־גְּב֥וּל אֱד֖וֹם בַּנֶּ֑גְבָּה קַבְצְאֵ֥ל וְעֵ֖דֶר וְיָגֽוּר׃
 Hebrew: וְקִינָ֥ה וְדִֽימוֹנָ֖ה וְעַדְעָדָֽה׃
 ע is generally treated as silent by Westerners, although it does have a subtle guttural pronunciation.