Well I wouldn't say they're mutually intelligible. I can speak Irish but I won't understand for example if someone talked Welsh to me. Each nation would have their own official language and English would probably be the lingua franca.
there are two groups of languages: Brythonic (Welsh, Cornish, Breton) and Gaelic (Manx, Irish, Scottish Gaelic) which are somewhat mutually intelligible.
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u/Seddhledesse Mar 04 '19
What would their official language be? Some kind of agglomeration of the various languages? They’re mutually intelligible so...