My novel is set in a fantasy approximation of 1250AD Europe.
As I write, I do a truckload of research of, "What words existed back then?"
I spend two weeks researching 'time'. I wanted to write, "Just a second" or "I'll be with you in a minute."
It turns out the concept of "minute" didn't exist until the 1500's and "second" until the 1700's.
I gimped it with, "Just a moment" and "I'll be right with you." (Researching "Moment" is a whole 'nother cup of worms.
Then I had lines like, "She inched forward." Inches didn't exist back then.
I was really trying to stick to the language of the time.
Then I wanted to say something like, "That was really weird." I researched the word. "Weird." It turns out it did exist back then, but it had a totally different meaning. It was a noun referring to, "someone that used magic to view the future."
So I made the choice... I can either write this in Old English... Or I can write this to my audience.
I try to keep the language to the time where I can, and I bend the rules where I need to.