That's a difficult question, but if a language changes rapidly then not everyone will keep up with the changes to the same extent and communication between thos

That's a difficult question, but if a language changes rapidly then not everyone will keep up with the changes to the same extent and communication between those people will be compromised. This also affects written communication. Most modern English speakers can't understand Shakespeare properly. They could, if they put in hundreds of hours of study, but in practice they don't. English hasn't changed very much over the last 100 years, I'd claim, compared with many other languages, but it's hard to measure that objectively. To start off with, what do I really mean by "English"? I suppose I mean the standard written language rather than colloquial forms... One could perhaps also argue that a language that has changed a lot recently can't have built up the vocabulary, connotations, and all the rest of the stuff that is required for high-quality, nuanced communication and is therefore likely to be a less precise means of communication even between people who are tracking the changes. But that's speculative and I don't know how you could measure it. So, to conclude this waffle, I suspect it does make sense to talk about a language "degenerating", but it's very hard to be scientific about it.