On the evening of that day, the first day of the week, the doors being shut where the disciples were, for fear of the Jews, Jesus came and stood among them and said to them, "Peace be with you." When he had said this, he showed them his hands and his side. Then the disciples were glad when they saw the Lord. Jesus said to them again, "Peace be with you. As the Father has sent me, even so I send you." And when he had said this, he breathed on them, and said to them, "Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained."
My own background on this issue--well before our journey to the Catholic Church--has also been a great influence. As my grandfather was a minister and my great aunt a medical missionary to Africa, this was an issue that came up from time to time. The Charismatic understanding of speaking in tongues always troubled them. I remember one account, for instance, of missionaries coming back from the field and visiting a church where speaking in tongues was being practiced. They hurriedly left, as I recall, because they heard most profane things being said in one of the obscure languages of the mission field.
When I worked in the late 1980s in Seattle for an Assemblies of God Church, I also had an experience that will always stick with me in a most negative way. I was on my way back to Seattle Pacific University after work and riding beside me was a colleague from the church. I remember as the bus neared the Freemont District where I would exit, my seatmate began to loudly "talk" about church and faith. He wasn't actually speaking to me at all, but was using me as an excuse to witness to those on the bus. We should all be willing and able to articulate our faith in public, but there is something very disagreeable about excited and disingenuous expressions of faith like this. Like the way I see many of those on the Charismatic side, their faith seems to my perspective to reflect something more akin to emotionalism than reason.
As we read in 1st Corinthians 14:28, speaking in tongues without an interpreter is contrary to the teachings of Saint Paul. Speaking in tongues, then, is a ministry tool (to address a specific manner of need in spreading the Gospel) which focuses more upon the hearer than the the speaker. That is, the speaker is trying to share the Gospel of Christ with someone of a different culture. The act of speaking in tongues is to convey the Gospel, as opposed to "puff-up" the speaker, conveying true humility rather than pride, and spreading and strengthening the people of God.
The above does not mean that all those who practice speaking in tongues are doing something wrong and contrary to biblical teachings, but it does, at the very least, suggest strong caution. I'll agree that it is a difficult and complex topic. There is, for instance, the case of Heidi Baker in Mozambique. Unless it's all a fabrication and a lie--which I don't propose--God is performing wondrous and powerful acts of healing through this diminutive woman. Of course, this is the mission field, the truly legitimate place for speaking in tongues. It's truly challenging to address such a deep topic in a blog post, but I offer my thoughts and reflections on this topic only as points for your consideration.
In conclusion, below is what the Catechism of the Catholic Church says on this important topic.
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.