Radak: Yisrael will come from all the four corners [of the world] in which they are scattered. The east is called me'Rachok, for Eretz Yisrael is roughly in the middle of civilization, and it is further from the east, for it a bit west [of the exact middle]. Malbim - in spite of the great Simchah of the gathering of exiles from the four corners, Tziyon is like a deserted widow mourning that her husband abandoned and forgot her. It does not know of all the Simchah in the world, until it lifts its eyes and sees the salvation.

Malbim: Me'Rachok is the exiles from the east, i.e. the 10 tribes. They were exiled far away.

Radak: From the west.

Rashi, Targum Yonasan: From the land of the south. Radak - Sinim dwell there. They are from Kena'an's sons, like it says ["v'Es ha'Sini" - Bereishis 10:17].