Short answers, pulled from the story.
The basic sounds and a handful of words for the Klingon language were devised by actor James Doohan and producer Jon Povill for Star Trek: The Motion Picture in 1979. Marc Okrand, who had previously constructed Vulcan dialogue for Star Trek II: The Wrath of Khan, was then commissioned to develop it into a complete language for Star Trek III: The Search for Spock in 1984.
Linguist Arika Okrent estimated in her 2009 book In the Land of Invented Languages that roughly 20-30 people could hold a genuine conversation in Klingon. A broader community studies and writes about the language through organizations like the Klingon Language Institute.
The Klingon Language Institute, or KLI, exists to promote the Klingon language. It considers only vocabulary and grammatical forms introduced by Marc Okrand to be canonical Klingon, and it provides a Learn Klingon Online lesson series to members, with early lessons available as a free sample.
At least nine works have been published in Klingon translation, including Hamlet, The Epic of Gilgamesh, Much Ado About Nothing, the Tao Te Ching, The Art of War, The Rime of the Ancient Mariner, The Wonderful Wizard of Oz, The Little Prince, and Alice's Adventures in Wonderland.
Duolingo opened a beta Klingon course on the 15th of March 2018. The course proved popular enough that Duolingo offered to promote it out of beta status, but the course developers declined until software issues involving Klingon's case-sensitive letters and its use of the apostrophe as a consonant could be resolved.
Klingon follows object-verb-subject word order, which is the reverse of English. Klingon is also agglutinative, building meaning through chains of affixes; verbs take prefixes indicating subject and object, and nouns take suffixes from five ordered classes covering grammatical number, possession, and syntactic function.