John Gill Commentary Zechariah 14:12

"And this shall be the plague wherewith Jehovah will smite all the peoples that have warred against Jerusalem: their flesh shall consume away while they stand upon their feet, and their eyes shall consume away in their sockets, and their tongue shall consume away in their mouth." — Zechariah 14:12 (ASV)

And this shall be the plagues
This respects one or more, or all, of the seven plagues, which will be inflicted on the antichristian states, mentioned in (Revelation 15:1-16:21) :

wherewith the Lord will smite all the people that have fought
against Jerusalem ;
who have been the enemies and persecutors of his church; and with which plague or plagues they shall be utterly consumed and destroyed:

their flesh shall consume away while they stand upon their feet ;
antichrist will be consumed with the breath of Christ's mouth; the flesh of the whore of Rome, which is her substance, shall be eaten and devoured by the kings of the earth; and her destruction will be in a moment, suddenly, and at unawares, as is here suggested; see (2 Thessalonians 2:8) (Revelation 17:16) (Revelation 18:8Revelation 18:10) :

and their eyes shall consume away in their holes ;
the right eye of the idol shepherd shall be utterly dried up, and the kingdom of the beast will be full of darkness, (Zechariah 11:17) (Revelation 16:10) :

and their tongues shall consume away in their mouth ;
with which antichrist and his followers have blasphemed the name of God, his tabernacle, and his saints; and which they will gnaw for pain, when the plagues of God are inflicted on them, (Revelation 13:5Revelation 13:6) (16:9-11) .