J. Michael Straczynski has a long post
It helped that George Takei was away at the time, filming The Green Berets alongside John Wayne. Koenig was given Takei’s lines in “Tribbles,” which explains how he knew about quadrotriticale (botany was one of Sulu’s hobbies). He was given Takei’s lines in other second-season episodes too, like 'I, Mudd" and “The Gamesters of Triskelion.”
Actually it was my favorite role of his
Same here. I speak Russian, though mine is quite stale, but no native Russian speaker I ever heard, had Chekhov’s accent when speaking English.
“Scotty” (James Doohan) was born to Northern Irish parents in Vancouver, British Columbia. So he’d normally sound like any other Canadian. I recall an actual Scottish friend, with a proper Scottish accent, remarking that TV’s Scotty sounded like nobody he ever knew back in Scotland. But once he got past that, he enjoyed “Star Trek” as much as anyone.