Judge me, O God, and plead my cause against an ungodly nation: O deliver me from the deceitful and unjust man. Judge me, O God, and plead my cause - ריבה ריבי ribah ribi, a forensic term, properly enough translated, plead my cause, be my counsellor and advocate.
Ungodly nation - The Babylonians; the impious, perfidious, wicked, and deceitful Babylonians.
The deceitful and unjust man - Nebuchadnezzar.