Relate this to the historical Assyrian and Nebuchadnezzar, the king of Babylon, coming upon Egypt to cause destruction. But for our times, in the near future, we know these are but a 'type' for the future king of revived Babylon, i.e. Satan himself as 'a spurious Messiah'.

Isa 19:18    In that day shall five cities in the land of Egypt speak the language of Canaan, and swear to the LORD of hosts; one shall be called, The city of destruction.

     This is future.... Five in Biblical numerics means 'Grace'. So 'five cities in the land of Egypt' means Egypt will receive God's Grace when Christ's Kingdom on earth is setup. All will return to the original language which all nations once spoke, before the tower of Babel event.

 

Zephaniah 3:9:

 

 Gen.11: Read All.

     This phrase "The city of destruction" is the proof for this prophetic interpretation. The word for 'destruction' was altered in the Manuscripts after Jerusalem had been cleansed, and restored to true worship. This city was Heliopolis, Egypt and had another Israelite Temple. The original Hebrew Manuscript word was 'cheres' meaning 'the sun', and referred to 'ha-zedek', meaning 'righteousness'. Couldn't have another Temple in Egypt competing with the one in Jerusalem, so some scribe evidently dropped the "c" off of 'cheres' (the sun) and made it read "heres" (destruction). The Hebrew Massorah of the Old Testament also locks in this meaning of 'righteousness'.⁴ the proper reading is "The city of Righteousness".
     The subject just changed from a punishment by God, to a time of His future Blessings upon Egypt!

Isa 19:19   In that day shall there be an altar to the LORD in the midst of the land of Egypt and a pillar at the border thereof to the LORD.
20    And it shall be for a sign and for a witness unto the LORD of hosts in the land of Egypt: for they shall cry unto the LORD because of the oppressors, and He shall send them a Saviour, and a great One, and He shall deliver them.

     Naturally, this verse has not happened yet with our Lord and Saviour Jesus Christ's return.
     This 'pillar' is the Great Pyramid in Egypt. Will it be restored to its pristine shape when our Lord comes, or at least when God's Eternal Kingdom is setup? It would appear so. That Great Pyramid originally had a golden Capstone for its Apex top. It's been missing for a long time. And the outer walls of the Pyramid originally had a highly polished limestone, smooth surface before Cairo was built (see Peter Thompkin's Secrets of the Great Pyramid.) Guess who that missingCapstone represents? That's right, Jesus Christ, our Cornerstone which the builders rejected.

     Here's a little titbit from Josephus about Seth and his sons as builders of two pillars, one of them in Egypt, written in Josephus' work The Antiquities of the Jews:

Now this Seth,(Son of eth Ha Adham) when he was brought up, and came to those years in which he could discern what was good, became a virtuous man; and as he was himself of an excellent character, so did he leave children behind him who imitated his virtues. (69) All these proved to be of good dispositions. They also inhabited the same country without dissensions, and in a happy condition, without any misfortunes falling upon them till they died. They also were the inventors of that peculiar sort of wisdom which is concerned with the heavenly bodies, and their order. (70) And that their inventions might not be lost before they were sufficiently known, upon Adam's prediction that the world was to be destroyed at one time by the force of fire, and at another time by the violence and quantity of water, they made two pillars; the one of brick, the other of stone: they inscribed their discoveries on them both, (71)

 That in case the pillar or brick should be destroyed by the flood; the pillar of stone might remain, and exhibit those discoveries to mankind; The Great Pyramid of Giza.