Star Trek: 10 Things You Didn’t Know About The Klingon Language
8. Don’t Sound Like A PetaQ: There’s No K In Klingon
When Okrand was first developing the language for Star Trek III, he paid close attention to what was said in the script – that Klingon was "guttural" – and added sounds accordingly. He also chose to deliberately violate certain "tendencies of human phonetics" in order to make Klingon feel more alien; each individual sound exists in a human language, but the group of sounds is unique to Klingon. Furthermore, he avoided the inclusion of 'z' and 'k' sounds as these were long associated with, as he puts it, "stereotypical sci-fi alien bad guys". To quote Okrand further, "not sure how Kirk fits into this".
There are a couple of fairly evident problems with the no 'k' rule: the name of the language/species itself, and the fact that a good majority of the (male) names of the Klingons in The Original Series began with a 'k'. Okrand stuck to his bat’leth (betleH), however.
He decided that what the Federation writes with a 'k' is firstly a mishearing of the Klingon sound written as q. The Klingon Language Institute describes this sound as:
Like English 'k,' but not really. […] [M]ade with the back of your tongue touching your uvula. It sounds a little like you’re choking.
Or, if you prefer, it’s a voiceless aspirated uvular plosive [qʰ]. Kor then becomes qor, Kang becomes qeng; Kahless is qeylIS, and so forth. There is another sound written with a capital Q* that requires even more spit to pronounce.
To say 'Klingon' in Klingon needs an additional sound, written with three letters – tlh – instead of the 'k' as in tlhIngan. This sound doesn’t exist in English, but it is a voiceless alveolar lateral affricate [tɬ], if you want to look it up.
You can find a more comprehensive guide to Klingon pronunciation in The Klingon Dictionary.
*Q in Klingon is a voiceless uvular affricate [q͡χ].