This quotation comes from Psalm 10.7.

Their mouths are full of bitter curses may be equivalent in some languages to “they constantly speak bitter curses” or “they fill their mouths with curses which are bitter.”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on Paul’s Letter to the Romans. (UBS Handbook Series). New York: UBS, 1973. For this and other handbooks for translators see here .