While the pronoun you is singular here, as in the previous verse, there may be a case for translating it as a plural in certain languages, since Ittai is the leader and representative of all the Gittite group. Later in this verse David tells Ittai to take your brethren with you. So translators may have to consider each pronoun in this verse separately to see whether it will be more natural to use a singular or plural in the context.
Wander: Goldman translates this verb “go up and down.” The Hebrew verb conveys the notion of moving from place to place with no fixed home base. The related noun is found in Gen 4.12 and 14. In 1 Sam 1.13 the same verb is used of the seemingly purposeless movement of Hannah’s lips. See also Num 32.13.
As in the previous verse, the question here is not asked in order to obtain information but to allow Ittai and his men the option of avoiding the uncertainty of wandering around with David and his forces. So it will be possible to translate “you [and your men] don’t have to wander around with us.”
Yesterday … today: these terms are definitely not to be taken in their literal sense. Yesterday refers to a relatively short time ago and today means “now.” It will be a mistake in most languages to translate these words literally.
Your brethren: this, of course, refers to Ittai’s fellow soldiers from Gath, the men under his command. It may be translated “your troops” or “the other men from Gath.” It is quite likely that these men joined David at the same time as their leader Ittai.
May the LORD show steadfast love and faithfulness to you: some modern English versions have a shorter benediction in place of this one. New International Version, for example, reads “May kindness and faithfulness be with you,” without any mention of the name of the LORD. This is because the Hebrew text has only the words “kindness and faithfulness to you.” There is no indication in the text that this is a kind of benediction. For this reason Goldman ties these words to the previous imperative and ends the verse “take back thy brethren with thee in kindness and truth.” Fox similarly says “return, and have your brothers return with you, (in) loyalty and faithfulness!” The longer form including the name of the LORD, which clearly makes this a blessing, comes from the ancient Greek version. Hebrew Old Testament Text Project and Critique Textuelle de l’Ancien Testament accept the suggestion that the words “may the LORD show” were accidentally omitted by a scribe and recommend this longer reading, giving it a {B} rating. Contemporary English Version proposes “I pray that the LORD will be kind and faithful to you.” The word here rendered steadfast love is the same as translated “kindness” in 9.1 and “loyalty” in 3.8 (see also 2.6; 7.15).
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on the First and Second Books of Samuel, Volume 2. (UBS Helps for Translators). New York: UBS, 2001. For this and other handbooks for translators see here .