He said: this pronoun refers to Joab, who was the subject of the verbs in verses 9-10. In some languages it will be necessary to state clearly to whom he was speaking, as in New International Version, Contemporary English Version, and New American Bible, as well as Good News Translation.

Too strong for me … for you: that is, if the enemy forces started to take the upper hand in the battle on either front, the stronger of the two Israelite forces would send some of its men to help the weaker force. In some languages it will be more natural to say “If the Syrians begin to win the fight” or, turning the sentence around, “If we start losing ground to the Syrians.” Similar language will apply to the last part, saying what to do if the Ammonites succeed.

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 .