The Gift of Tongues is one of the many gifts of the Holy Spirit.
It is closely related to the Gift of Interpretation of Tongues. When one speaks through the Gift of Tongues, another may understand what is spoken through the Gift of Interpretation. As with the other Gifts, we must have faith and trust in God, and use the Gifts to bring God into our lives and us into God.
1 Corinthians 12:8-11 mentions "...varieties of tongues...".
Here are some manifestations of these Gifts.
So, (my) brothers, strive eagerly to prophesy,
and do not forbid speaking in tongues,
but everything must be done properly and in order.
1 Corinthians 14:39-40
Biblical sources
1 Corinthians 14:2 -- For one who speaks in a tongue does not speak to human beings but to God, for no one listens; he utters mysteries in spirit. (that is, ...for no one understands...)
1 Corinthians 14:13-14 -- Therefore, one who speaks in a tongue should pray to be able to interpret. (For) if I pray in a tongue, my spirit is at prayer but my mind is unproductive.
It is a language of emptiness -- less of myself and more of God.
Romans 8:26 -- In the same way, the Spirit too comes to the aid of our weakness; for we do not know how to pray as we ought, but the Spirit itself intercedes with inexpressible groanings.
Acts 10:45-46a -- The circumcised believers who had accompanied Peter were astounded that the gift of the holy Spirit should have been poured out on the Gentiles also, for they could hear them speaking in tongues and glorifying God.
A form of prayer or devotion.
Praying in tongues, many have discovered, achieves something which praying in their own languages did not do. It is the prayer of the subconscious, expressing the inexpressible, enabling our whole being to reach beyond itself, to escape from its limitations into the vastness of God’s love. Christians who have received this gift testify that it helps them when their own words seem inadequate, or when they don’t know exactly what to pray for (cf. Rom. 8:26), (http://cccrsa.net/charismaticcenter/what-is-the-gift-of-tongues/)
Biblical sources
Act 2:1-41 -- This is the Coming of the Holy Spirit and followed by St Peter's speech at Pentecost. Many people who came from different places heard the apostles. Then St Peter prophesied/spoke to them. What do you think happened when those people went back to their hometowns? Would they have spread the Good News?
1 Corinthians 14:10-12 -- It happens that there are many different languages in the world, and none is meaningless; but if I do not know the meaning of a language, I shall be a foreigner to one who speaks it, and one who speaks it a foreigner to me. So with yourselves: since you strive eagerly for spirits, seek to have an abundance of them for building up the church.
Grace is first and foremost the gift of the Spirit who justifies and sanctifies us. But grace also includes the gifts that the Spirit grants us to associate us with his work, to enable us to collaborate in the salvation of others and in the growth of the Body of Christ, the Church. There are sacramental graces, gifts proper to the different sacraments. There are furthermore special graces, also called charisms after the Greek term used by St. Paul and meaning "favor," "gratuitous gift," "benefit." Whatever their character - sometimes it is extraordinary, such as the gift of miracles or of tongues - charisms are oriented toward sanctifying grace and are intended for the common good of the Church. They are at the service of charity which builds up the Church.
1 Corinthians Chapters 12 and 14 are about the Gifts of Tongues and Interpretation of Tongues.
Acts 10 tells an inspiring story of Cornelius and his household.
If I speak in human and angelic tongues but do not have love,
I am a resounding gong or a clashing cymbal.
1 Corinthians 13:1
St Anthony of Padua
Born in Lisbon, Portugal. Lived in Padua, Italy.
He preached in Italy and France while speaking their native tongue although he never studied those languages.
He was preaching one day before the Pope and the Cardinals in Consistory. There were therefore present at that moment men of different countries -- Greeks and Latins, French and Germans, Slavs and English and men of many other different languages and dialects. And being inflamed by the Holy Spirit and inspired with apostolic eloquence, he preached and explained the word of God so effectively, devoutly, subtly, clearly and understandably that all who were assembled at that Consistory, although they spoke different languages, clearly and distinctly heard and understood everyone of his words as if he had spoken in each of their languages. Therefore they were all astounded and filled with devotion, for it seemed to them that the former miracle of the Apostles at the time of Pentecost had been renewed, when by the power of the Holy Spirit they spoke in different languages. "And in amazement, just like in the Acts of the Apostles they said to one another: "Is he not a Spaniard?' How then are we all hearing him in the language of the country where we were born - we Greeks and Latins, French and Germans, Slavs and English, Lombards and foreigners?" (https://www.deepertruthcatholics.com/single-post/2016/06/10/The-Catholic-Defender-The-Biblical-Gift-Of-Tongues)
St Paul of the Cross
The grace of being heard at great distances was also documented on at least three occasions in the life of St. Paul of the Cross (1694-1775), the holy founder of the Passionist Order. Because of his extraordinary reputation for holiness, people would come from great distances to hear the man of God preach his missions, and to witness the remarkable miracles and cures that often accompanied his preaching. Therefore the crowds that gathered during his missions were often immense.
On at least three documented occasions, his voice could be heard by all those present, even amdst the usual noises of such a great crowd, extending even those who were literally several miles away. This extraordinary grace took place in the three locations of La Tolfa, at Civitacastellana, and on the Isle of Elba, where he was heard a full five miles away.
Also, as stated above with the Apostles and also St Anthony, it was also documented on several occasions that his Italian language was understood by members of different foreign nationalities and languages who had come to listen to him. (http://www.miraclesofthesaints.com/2010/10/speaking-in-tongues-supernatural-gift.html)
St Dominic
Born in Caleruega, Spain. Lived in Italy.
When in France, St Dominic with Bertrand of Garrega and some friends and disciples were singing litanies and reciting psalms and the divine office, which attracted two German pilgrims, who joined them. The Germans invited them to dine together. They were together for 4 days but could not understand one another. One the 5th day, St Dominic and his group knelt and asked God for the understanding of the language of the 2 pilgrims and that they may speak to the 2 about Christ. When they rose up, they were able to converse with them in German for the rest of their journey. (http://www.miraclesofthesaints.com/2010/10/speaking-in-tongues-supernatural-gift.html)
Saint Louis Bertrand (Luis Beltran)
A Spanish Dominican friar. He was sent as a missionary to the Caribbean Islands and Panama. While speaking to the natives in Castilian, he was understood by all and often spoke in languages with which he was naturally unfamiliar. (https://www.roman-catholic-saints.com/saint-louis-bertrand.html)
Saint Philip Benizi
Born in Florentine, Italy. A general superior of the Order of the Servites.
In the ecumenical council called by Blessed Pope Gregory X, St Philip addressed the full assembly of five hundred bishops, sixty abbots, and a thousand prelates plus two kings, many ambassadors of other kings, and an emperor. St Philip spoke and was understood by those who did not know Latin. (https://catholicism.org/council-father-a-saint-who-spoke-in-tongues.html)
Saint Francis Xavier
Born in Javier, Spain. A Navarrese Catholic missionary. Co-founder of the Society of Jesus.
St Francis Xavier evangelized in Goa, western India, with the help of an interpreter. He later travelled to the Pearl Fishery Coast of southern India where people spoke Tamil. He evangelized in Tamil fluently.
The east coast Indians, who spoke a different language, also understood him. A greater miracle was that these Indians had many doubts or questions and they heard the answers in their own language even though St Francis " was not addressing those questions in his discourse."
(http://www.stedwardcatholic.com/news/speaking-in-tongues-or-languages)
xenologia (Greek) - "foreign languages" or "foreign speech" - to be able to speak in foreign languages (1 Corinthians 14:10-12)
glossolalia (Greek) - "ecstatic speech" or "speaking in tongues" (glosso) - (1 Corinthians 14:13-14)