It's really weird, as it's almost like another language. Because I'm so used to seeing American spelling as well, I easily switch from one mode to the other. As you're likely not used to seeing regular English spelling, you wouldn't have been fluent in it so I can understand why it would be so hard for you. Yes, quite a few still needed to be corrected after your edits, but I've mostly automated that process with my own programming scripts since the bulk of my editors use American spelling.
For what it's worth, I was quite pleased that I was able to translate the explanation of the theory of relativity and am sorry it didn't flow to your liking But then, that's why I paid you all those peanuts to improve it.