Prithee, when thou hast characters which spring from time – Lo! – long gone by, take heed for thyself that thine own people might perchance yet understand their discourse.
For thou knowest or can surely surmise that the usual denizens of long ago who spoke with the lilt of yesteryear had not access to sufficient of the written word to spend their days in perusing it. Nor – and this, perchance, is the more salient point – nor will they deign to travel forward along the continuum of time for the purpose of comprehending and interpreting thy words for the ignorant amongst the present generation.
Thus we reach the sad conclusion that those of whom ye write cannot also read, while those who may read thy works are not those of whom ye write. It is therefore of necessity that ye write of those whom ye write, but to those who will read. This additionally requires those of whom ye write to adjust their diction accordingly, that those who will read may understand the words which they speak, which thou dost write.*
*Even old-time characters have to use modern English, or the modern English speakers - your readers - will have a hard time relating to them. Avoid modern idioms, modern slang, and references to things that date to modern times, but everything else is the same. K?