Anyway, if you're interested in Britain's Celtic heritage, there's a trilogy of novels by Peter May that take place in the Gaelic-speaking part of Scotland. The first one is The Black House.

but they have revived them. There are schools in both Cornwall and Isle of Man with primary schools teaching the language.

Thanks for the book suggestion! I'll put them on my list!

They've revived the core vocabulary and grammar, with a bad accent.

The language as a repertoire of stylistic varieties and speaking styles is gone. What's left is basically relexified English.

It's rather like Hebrew. Israeli Hebrew is older Hebrew "resurrected" in a sense, but the pronunciation and the underlying grammar--even a lot of the basic word formation processes--are different. They keep the form but the grammatical categories are skewed. (It's the same problem with modern Greek vs classical--they tried to keep the form, but the language was so different that it was almost a self-parody. Except in the case of Greek there was real continuity, so the language just evolved. In the case of Hebrew there was a real break. But now Israeli Hebrew's a honest to goodness living language, whatever its origins, while Cornish and Manx aren't. Even Scots and Shelta, two other languages mentioned, are barely viable. The writer is a "splitter," aiming to have as many languages as possible even if native speakers of the varieties don't see them that way.)

Another "it's rather like" is how I speak Spanish or even Russian. My pronunciation is off. My grammar is sometimes a bit wrong. But mostly what I say just doesn't sound right. Sure, it's comprehensible, but often it reflects influence from English or a lack of appreciation for different registers. Take a non-native speaker of English. "Pass the butter," "give me the butter," "hand me the butter," "butter, please," "relay the butter," "transfer the butter", "butter, now!" are all basically the same. The first is fairly formal, the second more preremptory, the third familiar, the fourth a bit jocular or used in a context with a lot of passing around of food items, the fifth sounds odd, the sixth odder, and the seventh is what you tell a kid to scold him when he refuses to yield the congealed cowmilk fat upon request. These are nuances, of course. My Spanish, their Cornish, is flattened. As with Israeli Hebrew, should it "unflatten" it won't be a lineal descendant of the state of affairs Cornish enjoyed until the 1700s when it croaked.