Well, it's hard to know, since most sincere Christians, like myself, don't personally know anyone who claims to speak in tongues in private prayer times. So they have little way to examine their lives too. I listen a lot to an online preacher who happens to claim he speaks in tongues in private prayer. Though I respect him, and think he does very well in his teaching on other bible subjects - I can probably have no way to know whether his assumption that he speaks in tongue is as true as he thinks it is, or not. He grew up in charismatic churches. But does not accept some of their teachings. Like he realizes that not all true Christians were said to be given the gift of tongues, whether for private prayer or for preaching to a gathering if an interpreter is present. I feel he does well by seeing that even if God still gives out the gift of tongues in some form, that God doesn't choose to give it to all Christians. He also sees that all Christians have the Spirit of God if they are true Christians, and I agree with that, too.
I have been exposed to charistmatic churches some in my past. But I don't think it is wise of Christians to pray for the gift of tongues, and then just automatically assume God will give that gift to him or her. That is not letting God decide, I feel. And also is in danger of giving into one's lively powers of imagination, if one isn't careful to not go ahead with it, unless they clearly feel the prompting of the Holy Spirit to do so.
I certainly know that there was a lot of speaking in tongues on the day of Pentecost, following soon after Jesus' ascension. But that may have been largely because there were lots of Jews from foreign lands, who needed to hear the gospel message in their own languages, in order to understand the preaching of the gospel, and to make the decision to accept and live by it in their lives.