Who came up with the spellings for all these names on Farscape?

They're not the most intuitive ones if you're assuming English orthography.

Rygel? Could be worse, but Rigel doesn't even get a redline, probably because i is more expected in that position.

D'Argo? What does the apostrophe mean? Don't talk to me about non-English phonetics, because with the translator microbes, who cares?

Zhaan? Quite aside from the oddly doubled a, that is NOT where I'd put the h. Zh, I typically assume when reading English, represents the sound in the middle of pleasure. (Edit: And here, the zh appears to represent the initial sound in zoo. Which ought to have been written as a z.)

Aeryn? I don't even know where to start.

But of course, these are all transliterations, aren't they? These folks don't habitually spell their names this way, they do it in some other alphabet. The person who came up with the spellings, therefore, must be the same person who came up with T'raltixx.

Is it possible that John Crichton simply can't spell? And if so, what should we make of this?

Well, I notice that most or all of his pop culture references are to things you watch or listen to, not books. I also notice that he's still dedicated to his tape recorder even though it's gotta be easier in space to get pen and paper than replacement cassettes and double A batteries. And he does have some weird inability to ever get other species names right, always adding in the wrong ending, which could indicate some phonological issues.

Conclusion: I think he might be dyslexic.

Secondary consideration: Dyslexia often goes hand-in-hand with ADHD. I can believe it.