The disciples of Jesus Christ after their baptism of the Holy Spirit on the Day of Pentecost began to speak in other languages. Obviously, to them, they were speaking in other tongues but in the ears of the people, they were hearing for the first time strangers who communicated clearly in their respective mother tongues.
The Holy Spirit intentionally changed their tongues-speaking into diverse tongues to further give a proof to the nations that Jesus came for all humanity and not only the Jews. Again, the Holy Spirit caused the people to understand the disciples in their own languages so to reverse the judgment that occurred at the Tower of Babel where the nations of the world got scattered.
In contrast, the Day of Pentecost united the believers in the Spirit of understanding to the praises of God while the Tower of Babel scattered the nations in the spirit of confusion to the praises of men. No wonder nations of the world as far as Egypt, Asia, parts of Libya, and even Arabs understood the language of the disciples.
To speak in people’s language is simply to understand and identify with people’s culture, norms and belief systems with the intentional purpose of influencing them for Christ. The kingdoms of the nations must necessarily become the kingdoms of our God and His Christ.
Henry Martyn, one-time world missionary, said that the Spirit of Christ is missions hence the nearer we get to Him the more intensely missionary we become. Christians who want to possess nations must be globally-minded in their local thinking.