Please back up what you’ve said here. There was a referendum on Welsh devolution, which only people in Wales voted for. There was a referendum on Scottish independence, which only people in Scotland voted for. Afaik there has never been a vote in Northern Ireland on independence / rejoining Ireland.
The vote on Catalán independence was held by the Catalán government, voted on only in Catalonia, Spain and it’s validity was rejected by the Spanish government. And Catalonia is not the only region of Spain to have its own language, and it’s very common for multiple languages to be spoken within a country, I’m not really sure what the relevance of that is here.