What Is It?
Gàidhlig is, of course,a Celtic language, derived from Old Irish. Nowadays it uses 18 of the 26 Roman letters - no j, k, q, x, y, or z. The pronunciation is mainly phonetic and, once you’re accustomed to the system, you should be able to read most words with ease. It has many nasal sounds; one lovely example is cnatan, meaning "a cold", which sounds nasal enough even before you throw in the stuffed nose!
As each language has its own idioms deriving from the surrounding culture, Gaelic has some lovely structures that native speakers tend to bring over into their English--e.g., "It doesn't put me up or down" meaning "It doesn't matter to me."
Since Gaelic has never been standardized, there are variations from one island or area to another in both pronunciation and, to some extent at least, in vocabulary, but these forms are mutually intelligible. An Irish speaker and a Scots Gaelic speaker have no major problems understanding one another, as the languages are still pretty similar.
The pronunciations given below are based mainly on Skye Gaelic: Apologies to any native speakers of other areas who feel they are misleading!