I want to write a novel set in the 12th century. I can learn about the platform for the story, like city life and culture of people at that time, by googling on the internet. But I don't know how to write the dialogues of characters at that time. I am unable to get the words to express the feeling of 12th-century people. I know it depends on the place of my novel. Suppose it's Greece. It's all fiction. But I want to show the feel.
I personally think the best strategy is to "translate" the speech of the past into the speech of the present. As far as I can tell, few readers want to struggle with realistic depictions of languages they have no interest in learning. Instead, they like placeholder words to imply historicity (e.g. "thou" and "thine"), which give the vaguest feel for the time as well as a quick reminder that the narrative is taking place in the past. Another technique (often used in movies) is to apply a common regional dialect/accent to analogous social positions in your historical setting (think of how many times Germans in American war films had British accents). It's not necessarily a fair way to do things (in fact, I don't know if I can even recommend it, I hadn't really thought about it before), but it seems (or seemed) to resonate with people.
Several decent paragons of English literature did the above with frequency:
- Shakespeare, who didn't bother much with dialectical veracity (see: everything he wrote that wasn't set in Britain)
- Virginia Woolf (in Orlando), who also didn't bother
- Robert Graves (in I, Claudius), who likewise didn't bother
Ultimately, choose a strategy that doesn't involve so much research that you never write that book.
This is primarily a stylistic choice.
The situation is this: accurately reflecting the speech patterns of the time is virtually impossible, would require absurd amounts of research, and would drive away any readers who don't have academic background in the period. Realistically, what you want to do is evoke the speech patterns of the period, without mimicking them perfectly.
The correct way to do this varies by your writing style, the genre and tone of your story, and the readers you hope to attract. Most importantly, it depends on what you feel comfortable writing. It may seem counter-intuitive to say that the amount of research you should do is determined by what you're comfortable writing, but at the end of the day it's your story and only you know what level of verisimilitude is right for it.
The bottom line: historical fiction is, by definition, a synthesis of the period it depicts and the period it was written in. This is not a bug, but a feature. How far you diverge from common usage will reflect how 'alien' you want the story to feel for a modern reader.
Cultural and location has a big impact on language. In Greece in the 12th century they definitely were not speaking English, which is what I assume you are writing in. If you want to capture the English style at this time from 1100 to 1300 is the period of Middle English. This is the period where you see the dropping from the various forms of ‘the’ and Old English word endings such as ‘es’ are tapering off and becoming more condensed and clear. I think if you really want to capture the tone of that century in dialogue you’ll have to put some research into Middle English. The Oxford English dictionary has a very detailed explanation and section on Middle English and explains the cultures that impacted the style at the time if you want to start there.