Dear 100 Hour Board,
Keltic or Seltic?
Dear King James,
While you are trying to figure that out, the Boston Celtics are kicking your trash.
-Sunday Night Banter
My first thought was that I hear "Seltics" for sports, "Keltic" for everything else, and that seems to be backed up by this Mental Floss article.
From the author, Stan Carey:
Growing up in the west of Ireland, I encountered the word Celtic at an early age. I should say words, because I spoke it differently depending on the context. Celtic had a soft c, like “Seltic,” in Celtic Football Club, and a hard c, like “Keltic,” elsewhere—Celtic mythology, Celtic music, The Celts.
But, this is the key takeaway at the end:
Critics are entitled to dislike “Seltic” or “Keltic,” but they have no business saying either pronunciation is wrong. Because they’re both right.