Mustered: see the comments on 11.8 and compare also verse 11 below.
Thirty thousand: the ancient Syriac text and one tradition of the Septuagint text read “three thousand,” which is the basis for the translations in New International Version, New American Bible, New Jerusalem Bible, La Bible du Semeur, Osty-Trinquet, La Bible Pléiade, and Stuttgarter Erklärungsbibel. The earlier editions of the La Sainte Bible: Nouvelle version Segond révisée translation in French have “a thousand chariots” here, but Nouvelle version Segond révisée joins those versions that have “thirty thousand.” Thirty thousand is an extremely large number. Critique Textuelle de l’Ancien Testament, however, correctly notes that such large numbers are part of ancient military narratives (see, for example, Josh 11.4 and Judges 7.12) and gives the Masoretic Text a {B} rating.
Some languages may have a technical term for soldiers who are horsemen. Compare “cavalry troops” (Good News Translation) and “cavalry” (Anchor Bible). There is some evidence to suggest that the horsemen were “charioteers” (New International Version and Klein), that is, those who drove the chariots. If this interpretation is followed, it may support the reading of the Septuagint that there were three thousand chariots, since it was common to have two charioteers for each chariot. See also comments on 8.11.
Troops: literally “people.” In this context the translation “infantry” (Revised English Bible) or “foot soldiers” (New American Bible) is preferable.
Like the sand on the seashore: this is a common biblical idiom for expressing huge numbers, so large that they cannot be counted (see Gen 22.17; Josh 11.4; Judges 7.12). The sand refers to the individual “grains of sand,” as Good News Translation makes explicit.
Michmash: see verse 2.
Beth-aven was a city in the territory of Benjamin near the border of the territory of Ephraim, between Jericho and Bethel (Josh 18.12). The name Beth-aven means “house of wickedness.” Amos (5.5) and Hosea (4.15; 10.5) ridicule the city of Bethel, which means “house of God” by calling it “Beth-aven,” that is, “house of wickedness.” Most likely the name Beth-aven here in verse 5 is likewise a derogatory reference to the city of Bethel. Traduction œcuménique de la Bible maintains the name Beth-aven in the text and observes in a footnote that this is another name for Bethel. A footnote is the only proper place for such information.
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 1. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .