Writing in the language of another time and place is challenging. There are several issues. One is accuracy and another is readability.

I taught myself to write broad Yorkshire for The Crack in the Lens and then found that more than half of my pre-readers could not read it. So I modified it before publication to something that retained the flavor but which more people could read.

In Part I of The Consulting Detective Trilogy the university undergraduates talk in a lot of slang. Some people have claimed that it is "too modern." That is not true. The slang was lifted from books written in the 1870s-1880s by recent graduates about their days at university, including one book by Arthur Conan Doyle. I checked anything I had doubts about with OED.

The problem is that people get an idea in their head about how people spoke at certain times. They are often wrong. For example, the British use the exclamation "Brilliant!" in a different way that Americans do but that usage only dates to the 1930s. So it has not place in a Victorian novel. On the other hand "Fits you to a T" sounds modern but dates back hundreds of years. It is so old that OED can't figure out what the T stands for.