The hypocritical nation spoken of is the kingdom of Israel. It is likely that at the time this prophecy was given, this hypocritical nation had already been sacked and taken northward. This is recorded in 1 Kings 17:6, ’In the ninth year of Hoshea the king of Assyria took Samaria, and carried Israel away into Assyria, and placed them in Halah and in Habor by the river of Gozan, and in the cities of the Medes.’ This is how the 10 tribes get lost; they are taken to the north by the Assyrians. Other than the description here, we have no idea where they have been taken. It is commonly understood that they were subsequently scattered all over the earth and probably a cohesive group was led further north.
"…the Other Tribes did become ‘lost’ to Judah’s record-keepers—not simply because they were taken captive, but also because they left their captivity and went forth ’into a land further distant,’ numerous of them undoubtedly choosing to settle in the lands through which they traveled.
“Since that time—particularly in the last few centuries—attempts to locate and identify the Other Tribes have been numerous. At different times and by a variety of Christian authors the Other Tribes of Israel have been identified with the Japanese, Chinese, Turks, Ethiopians, Persians, Yemenites, Nestorians, Afghans, Arabians, Britons, Kassites of Russia, Hindus and Buddhists of India, Scythians, Cimmerians, Celts, Kareens of Burma, North and South American Indians, Australians, and Eskimos. Indeed it is possible that remnants of the Other Tribes may have spread out and became part of all these peoples in fulfillment of the prophecies that Israel would spread itself throughout many countries.” (Vern G. Swanson, “Israel‘s ’Other Tribes,’ ” Ensign, Jan. 1982, 29–30)