a strange trend i see is to call english a "non-native" or "non-indigenous" language to britain, which is bizarre as the english language very much is from britain. the english language as we know it evolved here as a distinct language from what was spoken by the anglo-saxons who settled here, so i would very much say that makes it an indigenous language. a language that is native/indigenous to britain just mean that the language originates from britain, it doesn't necessarily have to also mean that the language is marginalised. and how far back are you prepared to go before something is no longer considered native to the area? the ancestors of speakers of modern celtic languages were likely from the european continent, and even further back both english and the celtic languages come from proto-indo-european, so are none of them "really" native to britain in that case, if they have a traceable root from somewhere else?
and it's strange bc english and scots both come from the same germanic roots, but i never see anyone claiming that scots isn't actually native to scotland bc of those roots. whereas some people (online and those i've talked to irl) are happy to claim that english isn't actually native to england bc it evolved from old english which ultimately evolved from the germanic languages brought over by anglo-saxons. and old english is also what scots evolved from, so scots shares those same roots.
i suppose maybe it's not that strange, bc the internet is very american, so i suppose people are taking the model of america and it's indigenous languages and applying it to britain, when it isn't exactly the same situation.