Albert Barnes Commentary Jeremiah 48:11

"Moab hath been at ease from his youth, and he hath settled on his lees, and hath not been emptied from vessel to vessel, neither hath he gone into captivity: therefore his taste remaineth in him, and his scent is not changed." — Jeremiah 48:11 (ASV)

Moab, from the time it conquered the Emims (Deuteronomy 2:9–10) and so became a nation, had retained quiet possession of its land and enjoyed comparative prosperity. From the Moabite Stone we gather that King Mesha, after the death of Ahab, threw off the yoke of Israel; nor, except for a short time under Jeroboam II, was Israel able to bring the Moabites back into subjection. They gradually drove the Reubenites back and recovered most of the territory taken from the Amorites by Moses, which had originally belonged to them.

He has settled on his lees - Good wine was thought to be better for being left to stand on its sediment (Isaiah 25:6), and in all cases its flavor was thereby made stronger (marginal reference). By being emptied from vessel to vessel it became vapid and tasteless. So a nation, by going into captivity, is made tame and feeble. By his taste is meant the flavor of the wine, and so it is with Moab’s national character.