Oh, my Lord is identical to verse 10. (See the comment there.) The expression that follows is difficult to understand apart from the context. Literally it is “please send by the hand of [whom] you will send.” Some translations may incorrectly suggest that Moses is finally accepting his new commission. (New English Bible has “No, Lord, send whom thou wilt.”) This is a final attempt of Moses to be relieved of such a responsibility. Good News Translation has “No, Lord, please send someone else.” And Die Bibel im heutigen Deutsch has “Don’t be offended at me, Lord, but still send someone else!” In languages that require special honorifics in this context, those should be used here. A way to do this in English is “Lord, please excuse me! Please send some other person.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .