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As for the practice of glossolalia being a private practice for self edification, prior to the charismatic renewal, it appears to have been a monastic practice for a long time - at least in the Eastern Orthodox tradition. Fr. Morton Kelsey wrote a book back in 1964 called, "Tongue Speaking: The History & Meaning of Charismatic Experience." In the book he writes about Greek Orthodox monastic practices:
Among some of the Orthodox clergy there is a sympathetic understanding of the practice of tongues, and I keep running across reports that it is known, and has been known through centuries in the monasteries. (p. 43)
If "jubilation" is a "de facto" unacknowledged species of glossolalia, then there are lots of references in church history to it being a form of private prayer. This would be despite the "de jure" view of many in the early church (Chrysostom, etc.) that the gift of tongues ceased to be given. Proverbs 25:2 states: "It is the glory of God to conceal a matter, and it is the glory of a king to search out a matter."
A good place to do some scholarly research is John C. Poirier's "Tongues of Angels: Concept of Angelic Languages in Classical Jewish and Christian Texts." Also, Eddie Ensely's "Sounds of Wonder, 20 Centuries of Praying in Tongues and Lively Worship."
In the early 20th century, the American Lutheran theologian, R.C.H. Lenski describes how non-conceptual sighs and groanings can sometimes be involved in intercessory prayer. In his commentary on Romans, Lenski rejects the interpretation that Romans 8:26 is a reference to literal sighs and groaning. However, in a type of admission against interest (as he was very concerned about the rise of the Pentecostal movement), he writes about that verse:
Later writers state that the charisma of tongues was a speaking in non-human language and either identify these βgroaningsβ with this non-human language or conceive of them as a parallel to it. (Interpretation of St. Paulβs Epistle to the Romans, p. 547)
Another Lutheran scholar F. E. Mayer, in his 1954 book "The Religious Bodies of America" writes the following about the gift of tongues:
In the words of St. Paul this charism is the least among several spiritual gifts, inasmuch as it does not edify the entire body and at best is a highly ecstatic form of prayer and praise for private use.
It is important to note that the word "ecstatic" was understood by the Lutherans as being more "esoteric" than a description of having an "out of control frenzy."
In the Lutheran tradition, the 19th-century theologian, George Stoeckhardt, writes about the ecstatic/esoteric nature of tongues in his "Exegetical Lectures on the First Epistle of Paul to the Corinthians." In a reference to 1 Corinthians 14:2-5 and the speaking of tongues, he writes (emphasis added):
Here the Apostle compares the gift of prophecy with speaking in tongues. In the latter gift, the Spirit moves the inner spirit of man to utter euphonious sounds with this tongue. It was an ecstatic form of speaking, which, however, was unintelligible both to the hearers as well as to the speaker himself.