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These issues regarding language, national identity, and politics are like politics anywhere, and there's no way to summarize here (nor is it necessary in a travel guide) all the views that exist. While a significant number of Catalonians are anti-Spanish (and feel opposed to Spain and the Spanish language), many are simply indifferent.
In tourist areas, almost all shops and bars have some English speaking staff. However, like in the rest of Spain, English is not widely spoken, though it's still more widespread in Barcelona than in the rest of Spain.
Your best goodwill in communication would be to try speaking in Catalan if you can. The locals learn both Catalan and Spanish in school (and are completely fluent in both), but Catalan is definitely the preferred language. Even for those who do not support independence from Spain, clearly Catalan is the first language, and if you can communicate with the locals in Catalan, this is really appreciated. While most locals understand that Spanish is more prevalent and are willing to converse with outsiders in Spanish, any attempts to speak Catalan will be met by smiles and encouragement, by and large. As such, visitors should make an attempt to say some basic greetings in Catalan, even if the rest of the conversation is held in Spanish.