It is a common question to ask whether there will the be one language in the kingdom of God on earth when Christ returns. Partly that is because of expecting the confusion of languages of Babel to be undone – as it briefly was at Pentecost in Acts 2. But partly also since Zephaniah 3:9 addresses the time of the Millennium, when Jesus Christ rules on and over the earth, and states:
“For then I will restore to the peoples a pure language, That they may all call on the name of the LORD, To serve Him with one accord.” (Zephaniah 3:9)
Associated with this is another verse in Isaiah 19:18:
“In that day five cities in the land of Egypt will speak the language of Canaan and swear by the LORD of hosts…” (Isaiah 19:18)
The prophecy being that all the Egyptians will speak the same language as those who will live in the land of Canaan. Possibly Hebrew, since Hebrew is a Jewish dialect of the West Semitic languages, the parent tongue Canaanite. But Isaiah does not actually specify the language directly.
Against this the idea of a “pure language” in Zephaniah could equally be symbolic, stressing the purity in worship. We don’t know.