When would it be correct to use this formulation, instead of Aibreán? That is a little more formal in English. Or are they trying to get use used to the dative?
Would I say 'my son was born in April' or 'my son was born in the month of April?'
And if I was being really pompous (not that I would ever be that good) and I was translating TS Eliott, would I translate 'April is the cruelest month' with 'Mí Aibreáin' or 'Aibreáin.'?
Aibreán and mí Aibreáin seem to be pretty much interchangeable. (Mí Aibreáin demonstrates the genitive rather than the dative.)
You could say either Rugadh mo mhac san Aibreán or Rugadh mo mhac i mí Aibreáin, Is í Aibreán an mhí is cruálaí or Is í mí Aibreáin an mhí is cruálaí. I don’t know if there’s a particularly literary way to express a month, but Mí na Bó Riabhaiche (“month of the brindled cow”) is an obscure reference to March.
Considering this article, https://en.wikipedia.org/wiki/Wasteland_(mythology) , I think your translating Eliot's "The Waste Land" into Irish might be more appropriate than pompous. From the article:
"The Wasteland is a Celtic motif that ties the barrenness of a land with a curse that must be lifted by a hero. It occurs in Irish mythology and French Grail romances, and hints of it may be found in the Welsh Mabinogion.
An example from Irish literature occurs in the Echtrae Airt meic Cuinn [The article sums up the pertinent part, but I'll not "spoil it" for you, here. ᵔᴥᵔ It's been at least 6 centuries, but maybe it's "too soon."]
Scholars of the earlier 20th century devoted much study to the Wasteland motif. ... one of the more popular works on the subject, From Ritual to Romance, ... is mostly disregarded today, though T. S. Eliot credited it as the source of the title and the largest single influence on his famous poem The Waste Land."
Just don't end your translation with "Shinty, shinty, shinty."