Glad that you emphasize it's Plaça del Sol, not Plaza del Sol or Square of the Sun
Catalan is not a dialect of Spanish, if anything it would be a dialect of Occitan. And seeing how condescending are hurtful you are trying to be I suspect you already knew that.
> Why do people waste their time with that?
It's the native language of ~5 million people. We learn it for the same reason Swedish people learn Swedish, Danish people learn Danish, etc. It's just the language we speak in our country.
There is already a de facto international language (which is not Spanish BTW), and we also learn it.