Ogham isn't a language, but an alphabet. There isn't much out there on it
either. Stuart Piggott in *The Druids* mentions it, as does T.G.E. Powell in
his book *The Celts. Rudolf Thruneysen in his book *A Grammar of Old Irish*
covers it a little. If you can find a translation of the Book of Ballymote, it
might help (that's where we get most of information on the Ogham from). But,
scholars are at odds as to just how accurate The Book of Ballymote actually is.
So it depends on how your interests go. The above is a way to go, if yours is
a purely scholarly endeavor. If you have an interest in modern Paganism, you
could read *The White Goddess* by Robert Graves, which is more poetically
inspiring than it is accurate.
Nigel Pennick's book *Magical Alphabets* is some where in between, and covers
Ogham as well as many other alphabets. It's scholarly, yet keeps in mind the
needs of the modern Pagan, and points out (usually) where scholarship ends and
creative re-creation begins.
I hope this helped