A description of the Klingon language can be found in Dr. Marc Okrand's book The Klingon Dictionary (Published by Pocket Books, Simon & Schuster, 1985, second edition with new addendum 1992, ISBN 067174559X). Other notable works include The Klingon Way (with Klingon sayings and proverbs), Klingon for the Galactic Traveler and the two audio productions Conversational Klingon and Power Klingon.
Three books have also been published in the tongue: Hamlet, ghIlghameS (Gilgamesh) and paghmo' tIn mIS (Much Ado About Nothing).
Some Trekkers take the time to learn it and at some Star Trek conventions you can hear enthusiasts use it amongst themselves. They often greet each other with the Klingon word "nuqneH" (literally: "What do you want?"), which is said to be the closest thing to a greeting that exists in the language.
There was an attempt by a male Trekkie to raise a child bilingually in English and Klingon; it was decided that the father would speak in Klingon and the mother would speak in English. A few years into its life, the child began rejecting Klingon and gravitating towards English. Klingon had lacked any words for things that were important in a baby's life, such as "diaper" and "pacifier". At the time, it even lacked words for many objects common around the house, such as "table".
Paramount owns a copyright to the official dictionary and other canonical descriptions of the language. Some people dispute the validity of Paramount's claim of copyright on the language itself in light of the Feist v. Rural decision, but no challenge has actually been brought to court.
A programming language called Var'aq was inspired by Klingon.
This is a tentative list of the SAMPA transcription of the Klingon phonemes as listed in Okrand's book. (As is standard in ASCII phonetic representation, <angle brackets> represent orthography whereas /slashes/ represent phonemes.)
SAMPA representation
(The value of "S" and "tlh" is not certain; can someone confirm or correct?)