"An chluas bhodhar a thugadh Colm do na litreacha sin, ainneoin gur fhágadar síoraí ag déanamh leanna ar uaigneas é." - The deaf ear Colm gave to the those letters, despite the fact they continually left him making a cloak on loneliness. ????

An chluas bhodhar - the deaf ear; figurative for ignoring something.

I don't know the word leanna. I'll get back on it.

"ag déanamh leanna" literally means "making beer" but I don't understand the context.

Colm ignored the letters although they always left him drowning his sorrows from loneliness.

??? Just a guess.

The term appears in the song "Buachaill ón Éirne"

"Rachfaidh mé amárach ag déanamh leanna fán choill,
Gan coite, gan bád, gan gráinín breac ar bith liom,
Ach duilliúr na gcraobh mar éadaigh leaba ós mo chionn,
's óró sheacht m'anam déag thú, 's tú ag féachaint orm anall."

Leanna is an alternative spelling of "lionn" - humour of the body (i.e. mood)

Colm ignored the letters, despite the fact that they left him in a deep mood of loneliness.

Correction: leanna is the genitive singular of lionn.

Aaaagghh!!! How could I be so stoopid. Anois tá lionn dubh orm fhéin nach bhfaca mé rud chomh soiléir sin. Caithfead cúpla pionta leanna a chaitheamh siar anois chun mo náire a mhaoliú beagáinín.

Nó a "mhaolú" fiú.

I had to look up leanna. Ó Cadhain stretcjhes anybody's vocabulary.

I'm still not convinced I've got to the heart of this idiom.

Dinneen gives "grieving" as the meaning of "ag déanamh leannta dubha" and solitude for "ar uaigneas"

So I propose:
An chluas bhodhar a thugadh Colm do na litreacha sin, ainneoin gur fhágadar síoraí ag déanamh leanna ar uaigneas é

Colm ignored those letters, although they left him grieving when he was alone.