The second person singular pronoun thou is emphatic in Hebrew. Revised English Bible attempts to represent this in translation by saying “You yourself.”
Separate them: In the context it is clear that the separation of the people of Israel is for the purpose of making them belong to God in a special way (to be thy heritage). Some other ways of speaking about this extraordinary selection are “singled them out” (Revised English Bible), “set them apart” (New Jewish Publication Society’s Tanakh, New American Bible, New Jerusalem Bible), and “chose them” (Good News Translation, New Century Version).
All the peoples of the earth: As in verses 43 and 60, the meaning is “all nations on earth” (Moffatt) or “all the nations of the world” (New International Version).
Thy heritage: See the comments on verse 51.
As thou didst declare through Moses is literally “as you spoke by the hand of Moses.” This is perhaps a reference to Lev 20.24-26, which speaks of the separation of the people of Israel from other nations.
Fathers: Since the events described here were many generations in the past, this will be more accurately translated “ancestors” (New Revised Standard Version) or “forefathers” (Revised English Bible).
O Lord GOD: This address to God consists of the two Hebrew words usually translated “Lord” and “LORD” in English (ʾadonai and YHWH in Hebrew) when they occur separately (refer to the discussion on “Translating Lord and LORD” in “Translating 1–2 Kings,” pages 11-12). When the two names occur together, some adjustments may need to be made. Compare Good News Translation “Sovereign LORD” and God’s Word “LORD God.” One African language says “Lord Yaawe.” Its occurrence at the very end of the prayer may be unnatural in certain languages. It has already been noted that Good News Translation and Bible en français courant shift it to the beginning of verse 52. New Jewish Publication Society’s Tanakh, on the other hand, places it toward the beginning of this verse, following the emphatic pronoun. And Revised English Bible has it in the middle of this verse. Translators should consider where such a use of the name of God would be most natural in their own language.
Quoted with permission from Omanson, Roger L. and Ellington, John E. A Handbook on 1-2 Kings, Volume 1. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here .