Zimrathâni (Av."Merindori", Q."Mîrenóre"), the "Jewel-land," was situated north of the Yellow Mountains and south of the Bay of Drel. Bound by the river Celiant to the west, the Onpu Mispír to the north, and the Sîresham to the east, it was an astoundingly flat coastal plateau occupied by Apysaic-speaking Aden and Drel tribes. (The urbane Adena comprised the majority).
Mirëdor seems to be a corrupt form of the Quenya name Mîrënóre, maybe a topographical name scholars of the Elendili used in old maps.It seems highly unlikely that the name was ever used or even known in the utter south due to the animosity of the Kingsmen for use of the elven tongues.Zimrathâni however is the correct translation of Jewel-Land into Adûnaic.
the Wild Lands south and East, Gazetteer by Pete Fenlon