Language shift over a long period of independent development

Question

Consider a planet initially colonized (1500 years ago) by a group of about 200.000 people.
To prevent ongoing interference/influence of the high-tech society from which they originally came they cut of all contact.
They have elected to "go back" to a more rural/pastoral lifestyle.
No electricity, combustion engines, steam-power, but they are by no means primitive.
They do have printing presses and retain knowledge of science as far as it is applicable to their tech-level. Education (roughly high-school level) is freely available to the entire population and literacy is nearly universal.
People travel widely across the planet. Most nations are located in the coastal regions of large island continents and there is a lot of trade by ship going on between the islands.

Special consideration: After these 1500 years the population has grown to about 25 million people.
Some of those people is a sub-species of man-kind that has a significantly longer life-span. 500 years in stead of the normal 100 years.
These people were already present among the original colonists. They can (and do) interbreed with the normal humans and the children have a 50% chance of being long-lived too. Being long-lived also occurs (about a 1% chance) as a spontaneous mutation in children of otherwise normal parents.
In total the long-lived ones make up about 2-3% of the total population.
These long-lived people are fully integrated into society. Due to their age they gather more experience over time and tend to congregate into important positions in society. Their long-term view of things is seen as an important stabilizing factor upon society. Normal people usually don't begrudge them their long life as they realize that it also has its drawbacks: E.g. to outlive your loved ones.

Initially the entire society spoke the same language.
What would have happened to their language after, say, 1500 years?
Would the language evolve into various regional dialects and from there into separate languages?
Possibly keeping their original language as the lingua franca of scholars, scientists and diplomats? (Just like Latin remained in wide-spread use in Europe until well into the 18th century.)
Would the presence of the long-lived people put a brake on language shift?
Are there other factors that would prevent significant chances to the spoken and written language?

Ideally I'm looking for a plausible reason that enables an anthropologist that visits the planet after 1500 years (and who is reasonably capable in the language of 1500 years ago) to understand the locals and could blend in so he/she is able to travel around incognito.
(With blend in I mean: The locals thinks he/she has a funny accent, but it's close enough to let them think he/she comes from a nation on the other side of the planet.)

Answer 1

It may change some, but probably not so much as, say, Latin has evolved into different languages for the last fifteen centuries.

The key difference is the cultural/technological level of this colony:

• There will be a defined standard of what is the language, how each word is written and pronounced.

• All the people will have some formal schooling to know such an standard.

• Groups of people will be less isolated than hamlets and villages were at 500 AD. This means that "localisms" will be kept to a minimum, because they would interfere with communication with the rest of the community (in 500 AD it did not matter because there was not much communication outside a regional area).

• People will have easy access to books, films and songs written by their ancestors. Since for the suggested lifestyle I do not expect too much cultural production, most of the old works will not be displaced by new ones.

Also, there would be no foreign influences. No invaders, no traders which bring other words.

And of course, your elders will become and stabilizing factor, as people is less likely to change how they speak a language after they left childhood, so these elders will keep the use of the original version of the language useful.

Answer 2

Languages change in reasonably predictable ways. Knowing and understanding these principles allows us to follow language families back into the remote past, for example understanding how English and Sanskrit are related and going back in time to @ 3500 BC to reconstruct the Proto Indo European (P.I.E) language.

So understanding how the language will evolve in the future requires knowing some basic principles. In general, people tend to be lazy, so words, word structure and grammar tend to become simplified over time. Grimms Law supplies a set of metrics to track (or predict) the way languages change over time as a well known example. There is in fact an entire science behind this today.

An interesting website which discusses this in depth and provides speculative examples of how the English language might change is here: FUTURESE, The American Language in 3000 AD.

While I have no first hand knowledge of how oriental languages and language families evolve, we can infer that similar rules probably apply to languages like Chinese, and after 1500 years the colonists from China will also be incomprehensible to contemporary Chinese speakers.

Answer 3

After 1500 years the language would be so different that while you might still catch a word here or there you would most definitely not pass off as a native speaker (even one with a funny accent). After all, Italians can hardly be said to still speak Latin, even though the languages bear some small similarities.

I also feel that Latin as a lingua franca comparison is a moot point. Sure, it is a language that is still heavily referenced in Law and Science, but how many people actually speak it, as opposed to simply knowing some quotes and phrases?

For your traveler to fit in he would have to stop someone (at a remote farm, for example) and spend a few weeks learning the modern language.

His knowledge of the ancient version might serve as a decent foundation for the grammar of it, however.