How long will it take to form a new dialect and language in underground steampunk London?

Question

This is the start of an experiment to see just how useful Worldbuilding Stack Exchange can be. I'm planning a work of fiction, but rather than build the world around the story, I'd like to write the story in the world - in other words, making the setting without thinking about how it will be used. To do it, I'd like to ask a series of questions on Worldbuilding that touch on different aspects of it - using the site to help me better hone the various facets of the setting.

This is the first question.

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The setting so far is Victorian London - with a twist. Around the year 1850, massive coal deposits were discovered underneath central London (construction on the London Underground began roughly 15 years before it did in our world, and large-scale excavations started up quickly). Within five years, even larger seams had been found, and it became apparent that London was sitting on top of the largest coal seam discovered to that date.

By the year 1895 - the date of this story - the Underground project has expanded in conjunction with new mining enterprises, and there is effectively a second city underground, populated by workers and their families. I'm not entirely sure how deep it will run - certainly many hundreds and hundreds of feet - but it is quite sprawling.

The world underground is much different from the world aboveground, and as mining is the predominant occupation below the surface - at least, at first - it dominates society in a number of ways. For example, there have been changes to the language (English, of course) because slang terms have made their way into everyday speech. Here are some examples, based on their fictional technology:

• "vehicle" $\to$ "c'lagon", an effective contraction of "coal wagon" that was generalized to most wheeled vehicles.
• "lamp/light(bulb)" $\to$ "geordysword", reflecting an affectionate nickname given to a variant of George Stephenson's lamp that became common in this world.¹

I'd like to use common patterns in the jargon to create names, using in part some of the techniques suggested in Are there techniques for creating alien or foreign sounding names?. However, to do that I need to better understand the evolution of this new dialect/language to determine how much mixing is likely to happen, and on what timescales.

How long will it take jargon to turn into a dialect, and a dialect to then turn into a language? It is realistic to expect a new dialect to form in 50 years, under these conditions?

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^{1 This is in part an nod to the miners of Northumberland, though this term was never used ("Geordie" was and still is). The Stephenson lamp is one tie between the real world and this one.}

Answer 1

Ah but you already have a ready-made one... the Thieves' Cant

I think you may want to take a look at the Thieves Cant, as beautifully illustrated in Cant - A Gentleman's Guide: The Language of Rogues in Georgian London, by Stephen Hart.

While that was the language of a more metaphorical underground, it should serve as a useful guide, and is great for inspiration to create a credible past. It seems to have evolved in about 30 years, as a reaction to the creation of the London police force. So well within your time-frame.

A few interesting features:

1. Numerous synonyms for relevant terms, just like the Eskimos' alleged 40 words for snow. Consider the sheer number of synonyms for the word “steal”: Cloy, Do, Filch, File, Fleece, Give it to, Heave, Knap, and a dozen others. Or the myriad ways of referring to gallows: Chates, Crap, Gregorian Tree, Morning Drop, etc.

2. Sets of replacement words for generic nouns and verbs: 'ken' meant 'place', 'cheat' meant 'thing', as in "bleating cheat" would be a sheep. "Fake a ken" meant to "rob a place."

3. Most slang words are short (and sweet) 1 or 2 syllables at most, and yet are recognizably English: One can "snilch" or "york" at something and then decide to "fam" something, "milling" the victim if needed.

4. Lots of derogatory words for upper classes, cops, women, various minorities, ugly people, you name it. You don't wanna come across as a "Twiddle Poop" for instance.

Now this dialect was made specifically to be difficult to grok by outsiders. Since you don't want your readers totally lost, you may want to introduce them more gradually to the dialect, perhaps through the eyes of some outsider interacting with someone who straddles both worlds.

Answer 2

There is a precedent for this, and it holds up well to what you are looking for.

Cockney rhyming slang arose around the 1840s and became well established in only 20 years. It is completely impossible to understand unless you know it despite being mostly English words...

https://wikipedia.org/wiki/Rhyming_slang

It remains a matter of speculation whether rhyming slang was a linguistic accident, a game, or a cryptolect developed intentionally to confuse non-locals. If deliberate, it may also have been used to maintain a sense of community. It is possible that it was used in the marketplace to allow traders to talk amongst themselves in order to facilitate collusion, without customers knowing what they were saying. Another suggestion is that it may have been used by criminals (see thieves' cant) to confuse the police.

Answer 3

Well, to have an historical reference, at the time of the fall of the Western Roman Empire, Latin was far from being spoken uniformily through all the territories. Yet, with invasion from different groups and all that, its successors began to be considered different languages several centuries later.

Another example is that at the time of independence, South American Spanish was considerably different from European Spanish, yet they are still considered universally the same language.

Language evolution is a very slow process... think that people sheldom change their language after they reach puberty, and that kids todays will still be heavily influence by the language in people in his 50s.

A way to improve the speed would be mixing in your population groups that come from different backgrounds, so they end creating a creole or patois mixup language, but it would still need about one hundred years (and a society very isolated from the rest of London) to become their "mother language".

Answer 4

I don't think there's a hard and fast answer to this one, it depends in large part on how much contact the "underworlders" have with speakers of the mother tongue, if someone is constantly dealing with native speakers of mainstream English then you're not going to see their use of the language change much. Isolated populations will undergo change much more rapidly as slang terms come into common usage and then become fixed as daily terms. This process generally still takes decades but can be more rapid if it's deliberate on the part of the speakers, a deliberate effort to set themselves apart or to mimic an existing dialect that they view as prestigious.