Casadh an tSúgáin
I haven’t seen Brooklyn yet,
but I’ve watched all the clips on YouTube and what did I find?
Iarla Ó Lionáird singing Casadh an tSúgáin!!!
He plays a character named Frankie Doran. He flies by in the trailer at 0:37-0:41
I knew my Gaeilge would come in handy.
You can see all the words from the Iarla Ó Lionáird version of the song as recorded by the Gloaming at: https://ancroiait.wordpress.com/2015/09/16/461-casadh-an-tsugain/
I found a book on Munster Irish which helps a bit. Hint: Do=affirmative verbal particle
Here you have a translation of a different-but-definitely-related version of the same song.
And here is that version sung (surprise) by Muhammad Al-Hussaini, from Westminster Institute in London (he also is playing the fiddle). As one commenter said "Nil se go dona."