Sorry but the Celts did have a form of writing.  It was called Ogham or Ogam
and developed a few centuries into the Christian era.  The later switched o
the latin alphabet.  It's worth noting that the Celts of Julius Caeser's time
didn't have a written language, which is probably where this misunderstanding
came from.
  Latin or Greek are probably better choices for langauges, anyway.  Dr. Tofu
might be able to read them with a little trouble, which would avoid the
problems with Ranma the scholar.

Kent Hyam