I'd rather not frame it either way. I'd rather use the words to describe actions regardless of what my cultural or linguistic biases might try to dictate about those actions.
Klingon is not a technical or programming language; it does not express objective truths beyond cultural or linguistic biases. It has those biases built in on purpose, and many of the words Okrand gives us come with some kind of cultural or linguistic note on their usage.
There are things you can say in language that you're not supposed to say. You can say "We am thy freighter, Urva," and get your point across, but you've said it wrong. You've chosen the wrong verb form, used an archaic pronoun, and chosen the wrong determiner. It's understandable, but it's not right. You can't always choose a synonym when that synonym isn't used the same way, even if it refers to the same action.
Well, if we suppose for a moment that nga'chuq is used for people (or language-users, or whatever) and ngagh is used for animals (or non-language-users, or whatever), then saying luqara ngagh qeylIS is wrong. It's understandable, but it's the wrong verb.
mayqel's question is are ngagh and nga'chuq split like that, is there some other difference, or is there no difference at all?
The answer is we don't know. The English glosses aren't enough to
determine this. The reason he probably thinks this might be the
split is because in English mate is something animals do,
while have sex is something people do, and this is how the
glosses were given to us. Whether the Klingon usages of the words
matches the English usages of those phrases, we don't know. Star
Trek makes this determination even murkier, since aliens are often
said to mate with each other, while Terrans are not.
I gave my opinion on the difference between the two words, but you ignored that part.
You gave your speculation, for which you seem to agree we have no
evidence. I didn't see any reason to comment on that. For your
part, you ignored my request to provide an example of how someone
in the mainstream would use the word mate to refer to
people having sex.
-- SuStel http://trimboli.name