> I might as well describe my particular scenario in case anyone on the
> list thinks its relevant:
> I'm writing a pair of stories that take place five thousand years
> apart. The people and the country are the same. The people
> (human-like, not dragons or anything) live, on average, 1000 years.
> Humans are a minority in their part of the world, so I don't think
> they would have much of an affect.
It's an interesting situation to speculate on. Here's my take: consider
that humans average 3-4 generations per century. Then assume your immortals
average 3-4 generations per _millennium_.
5 millenia = 15-20 generations :: 5 centuries human, ditto
For human languages, that puts us back in the 16th Cent., 1500s; Engl. and
Spanish (the ones I know best) of that period are certainly readable, but
would probably sound rather strange (Engl. moreso than Spanish I suspect).
By the end of the cent., both are quite readable (cf. Shakespeare and
Cervantes; Engl. would still sound strange). How about 16-17th Cent.
Assuming your immortals' culture is literate and perhaps rather static, my
guess would be that there'd be probably minor changes in pronunciation only.
Probably new vocab. to keep up with technological innovations. Some factors
that might upset this conservative scheme: revolutions, dynastic changes,
migrations (whereby in such cases a previously non-standard or stigmatized
dialect might become favored)... etc.
> I simply use a natural language as an example, calculate the
> generations, and scale up the number of years to fit?
That's what I've assumed. It depends on your people reproducing at a slow
rate. Even if they don't, with many generations in contact, there would be
some need to maintain communication.
> language change continue at a similar pace, because people's language
> evolves continually throughout their lives, not just primarily at one
> stage of it?
Personally I feel it takes quite a jolt for a person's language to change
noticeable within their lifetime. (Excluding emigration to a foreign
country, of course.) The principal factor would be exposure to a dialect
that is perceived as more prestigious than one's own.