Do you know any books relating to how we alter our speech depending on the people we speak to?

Answer 1

Not a book but I would consider doing some research on "code switching" or "cross-cultural code-switching" specifically within intercultural communications! In some contexts, code switching may mean switching between languages, dialects, and accents but can also literally mean switching the way we communicate and how by using different types of wording, behaviors, and demeanors with different types of people so that anyone can fit in to a conversation regardless of their class or educational level (to give an example).