You know the fiction-writing dictum “Show, don’t tell.” But how does it apply in practical terms when it comes to communicating characterization without exposition?
People in different eras have unique speech and speech patterns, but restrain yourself from indulging in periodization in your historical novel; if your Elizabethan-era characters talk like Shakespeare’s, people 1) won’t understand much of what they say and 2) will be distracted by your forced — and fatally flawed — attempt at authenticity.
Do, however, immerse yourself in that period’s society: What did people know about history and sociology and psychology and spirituality (even if they didn’t use those terms to identify them)? What were prevailing political and social and religious viewpoints? How open were people about expressing themselves? Be careful not to let modern sensibilities intrude on the way your characters speak and think, but do permit them and their speeches and thoughts to be accessible to modern readers.
The extent to which characters will express their ideas and opinions, or ruminate about them, and the language with which they will do so, depends on a few other factors:
People of different generations and different social backgrounds generally speak differently. Geriatric characters should exhibit speech and speech patterns distinct from juvenile ones and consistent with norms unless an exception is a deliberate dramatic point — for instance, if a teenager who has switched bodies with an elderly person is trying to pass vocally as well as visually as a senior citizen.
Likewise, the speech and thoughts of well-educated characters will usually be distinguishable from that of those of others with less formal schooling. Of course, no one should assume that a person with only a high school education is less intelligent than a college graduate, or the reverse, but their vocabulary and the level of sophistication of their thoughts will, unless they are self-educated, likely differ.
Further individualization of characters makes fiction writing more vivid. How does one’s personality affect words and thoughts? A repressed person’s speech patterns will differ significantly from an extrovert’s. A tense, angry character will exhibit different rhythms of speech and thought than a carefree individual.
Length of speeches and thoughts is also a consideration: Children do not soliloquize, and philosophically minded people do not tend to make snap judgments. Match the extent to which people speak and think to their personalities. But keep in mind that various sentence lengths and paragraph lengths have differing dramatic values, too — long passages tend to be soothing (but, when too long, are soporific), while short bursts create or maintain tension (though, in excess, can be just as wearying as extensive paragraphs).
In essence, capitalize on your knowledge of individual characters to establish vocabulary and modes of speech and thought, as well as on familiarity with societal norms for speaking and thinking appropriate to the era in which your characters live.