Valencian/Catalan is actually one single language, although you can use either term to refer to it.
There are two main dialects of the language (eastern and western) but their division is by geographic borders, rather than by administrative divisions.
https://en.wikipedia.org/wiki/Catalan_language
There is a nationalistic political movement called "Blaverism" that states that people in Catalonia and in the Valencian Community speak different languages, but their reasons are political, not linguistic.