As a polyglot and teacher, Devlin was particularly known for his work in French and in Irish. For many years, he was rector of the
Irish College in Paris and also published three novels in Irish:
Néal Maidine agus Tine Oíche (1964),
An Branar gan Cur (1979), and
Sliocht ar Thír na Scáth (2018). He has also published translations from French into Irish by La Fontaine, Pascal and Saint-Exupery. He translated several books of the Bible into Irish. In addition to French, Devlin learned Polish, reputedly for use in the negotiations involved in bringing the Irish College in Paris back from the control of the Polish church who had used it for many decades. In total, he spent 74 years at Maynooth College. ==Irish College, Paris==