Unity comes from our baptism, not from using a common language. I Corinthians 12:13 makes it clear that “by one Spirit we were all baptized into one body, whether Jews or Greeks, whether slaves or free, and we were all made to drink of one Spirit.”
Reciting one language is “unison,” not “unity” or “unifying.”
When we pray, the Holy Spirit prays for us in groans and “words” that we can’t hear or understand. So no matter what languages we all pray in, we are “one” because of the work of the Holy Spirit.
Corrie ten Boom wrote a book about her experiences in Ravensbruck concentration camp (she and her sister were arrested for giving shelter to Jews). In Chapter 13 of the book, she describes a prayer meeting in Barracks 28: “A single meeting might include a recital of the Magnificat in Latin by a group of Roman Catholics, a whispered hymn by some Lutherans, and a sotto-voce chant by Eastern Orthodox women. With each moment, the crowd around us would swell…at last…I would open the Bible. Because only the Hollanders could understand the Dutch text, we would translate aloud in German. And then we would hear the life-giving words passed back along the aisles in French, Polish, Russian, Czech, back into Dutch. These were little previews of heaven…”
You see, these Christian women were One in Christ, not because of a language. In fact, their languages were all different. They were One in Christ because the Holy Spirit was in them, helping them to love and support each other in the worst circumstances imaginable. And other women were attracted to the Christians because of the love and light that shone strong from these Christians.
Non-Christians and fallen-away Christians may or may not be attracted back to Christ by human practices like Latin, vernacular, chant, or rock music. But according to the Word of God, they WILL be attracted back to Christ by our active love for one another.