That is because his mother Mary Anne MacLeod, pictured, was from the Hebrides, off the Scottish Highlands coast, where Gaelic was spoken by both of her parents, who passed it on to her.
Mary Anne was born in the Hebrides in 1912 and moved to America where she met and married Fred Trump, Donald's father. She brought Donald back to Scotland when he was very young. He has since visited with his sister.
As a Scottish heritage site put it:
"Mary Anne was born in the village of Tong, in the parish of Stornoway on 10th May 1912, to a fisherman named Malcolm MacLeod and his wife, Mary Smith.
"This couple had been married in 1891 and both were Gaelic speakers, and, although not so widespread as it once was, the language is still alive and well in that region.
"It is thus likely that Mary Anne herself would have spoken it and the young Donald may well have been soothed by Gaelic lullabies as a child."
Charming notion that the man who is be best known for saying 'you're fired' might also be capable of remembering Gaelic words taught to him as a child.
Well he should certainly learn 'Pog mo Thoin' which means of course 'kiss my a..'
He has aimed that barb at plenty of opponents, I'm sure.