Languages of Catalonia
According to the official government of Catalonia, Catalan is the second most spoken language of the region, after Spanish (over 35% of Catalans use exclusively Catalan as their first language, while 11% of Catalans use equally both Catalan and Spanish). It is the most spoken language in many comarques of Catalonia, with the exception of the Barcelona metropolitan area (Barcelonès plus surrounding comarques) and Camp de Tarragona. Catalan is a compulsory subject in schools and enjoys equals rights with Spanish throughout Catalonia.
Province of Castellón
It is a bilingual territory whose inhabitants speak both Spanish and the local co-official language of Valencian/Catalan. Although Spanish and Catalan are closely related comprehension is limited: the language is a 'bridge' between Western Iberian and Gallo-Italian. There are marked distinctions in vocabulary and grammar which puts Catalan closer to Occitan in southern France and Italian (in frequently used words) which make it difficult for a monolingual speaker of Spanish to understand. Usage is a source of some controversy and political but not to the degree as in Catalonia.