Spent a few hours going through the fantasy novels and harmonizing my use of titles. It's hard to invent a whole new world, right down to the conventions of social address. Worse, if you do invent too much, you just confuse and annoy the reader. So you have to use the existing framework that everyone already knows (which is itself difficult since they only know that framework from books) but change enough that readers don't question why your wizard is talking like a 17th century Frenchman.
But formal rules aren't enough; real people bend their language, twisting it to different ends: intimacy, hostility, flattery, contempt. I had to make charts listing each major character and how they address each other to keep it all straight.
I doubt any reader would consciously notice all this work, but I think subconsciously they do. When you spend enough time with a character, you expect them to behave and speak in a different way: the worst crime an author can commit is to rob his characters of their unique voice.
Fortunately, the craft of writing is mostly smoke and mirrors, and the author can get away with a lot. In the process of rewriting I've put speeches from one character into another character's mouth, only needing to change a few words to change the owner. The king of this technique is Peter Jackson, who transferred an entire speech, word for word, from one of the worst bad guys (Wormtongue) to one of the best good guys (Gandalf). But he had intonation to work with, changing the tone from sneering to pitying. My only tools are letters, blank spaces, and punctuation marks.