As noted above, it is by Charles Badger Clark, titled A Border Affair. The first verse-

Spanish is the lovin' tongue,
Soft as music, light as spray.
'Twas a girl I learnt it from,
Livin' down Sonora way.
I don't look much like a lover,
Yet I say her love words over,
Often when I'm all alone-
"Mi amor, mi corazon."

Various covers, with variations, by several singers.

All this has been covered in another thread.