Anyone who is against the behavior of the Vedic principles is called a yavana. Such a yavana may be in India or outside of India. As described here, the symptom of yavanas is that they are violent killers of cows and brahminical culture. We offer our prayers to the Lord by saying, namo brahmanya-devaya go-brahmana-hitaya ca. The Lord is the maintainer of brahminical culture. His first concern is to see to the benefit of cows and brahmanas. As soon as human civilization turns against brahminical culture and allows unrestricted killing of cows, we should understand that men are no longer under the control of the Vedic culture but are all yavanas and mlecchas. It is said that the Krsna consciousness movement will be prominent within the next ten thousand years, but after that people will all become mlecchas and yavanas. Thus at the end of the yuga, Krsna will appear as the Kalki avatara and kill them without consideration.

From Srila Prabhupada’s purport to Cc Antya 3.50