Visvamitra, being angry, cursed them. "May all of you bad sons become mlecchas," he said, "being opposed to the principles of Vedic culture"

Expressions researched:
"Viśvāmitra, being angry, cursed them. "May all of you bad sons become mlecchas," he said, "being opposed to the principles of Vedic culture"

Srimad-Bhagavatam

SB Canto 9

When requested by their father to accept Śunaḥśepha as the eldest son, the elder fifty of the Madhucchandās, the sons of Viśvāmitra, did not agree. Therefore Viśvāmitra, being angry, cursed them. "May all of you bad sons become mlecchas," he said, "being opposed to the principles of Vedic culture.".

SB 9.16.33, Translation and Purport

When requested by their father to accept Śunaḥśepha as the eldest son, the elder fifty of the Madhucchandās, the sons of Viśvāmitra, did not agree. Therefore Viśvāmitra, being angry, cursed them. "May all of you bad sons become mlecchas," he said, "being opposed to the principles of Vedic culture."

In Vedic literature there are names like mleccha and yavana. The mlecchas are understood to be those who do not follow the Vedic principles. In former days, the mlecchas were fewer, and Viśvāmitra Muni cursed his sons to become mlecchas. But in the present age, Kali-yuga, there is no need of cursing, for people are automatically mlecchas. This is only the beginning of Kali-yuga, but at the end of Kali-yuga the entire population will consist of mlecchas because no one will follow the Vedic principles. At that time the incarnation Kalki will appear. Mleccha-nivaha-nidhane kalayasi kara-bālam. He will kill all the mlecchas indiscriminately with his sword.