Catalan, the language, does not have a flag. As a native speaker (of a dialect) who is not from Catalonia I would much rather the language be represented by the Spanish national flag. Although people from Andorra might also not love that.
Languages and flags don't mix well.
I am not sure if I got you, are you aware of the cultural/political issues around it? There's no flag for the language (as it's used at many places), but almost everyone will be happy with a commonly known flag they can identify with. A Valencian will be fine with a Catalunya flag :)
Academically, maybe it doesn't have a flag. But the de facto flag is the Senyera and I don't think a lot of people wouldn't recognize it as such in Spain.
I wonder if anyone ever came up with logos or at least emoji codes for languages?
All the areas where Catalan is spoken as a mothertongue:
- https://en.wikipedia.org/wiki/Alghero
- https://en.wikipedia.org/wiki/Andorra
- https://en.wikipedia.org/wiki/Balearic_Islands
- https://en.wikipedia.org/wiki/Pyr%C3%A9n%C3%A9es-Orientales
- https://en.wikipedia.org/wiki/Catalonia
- https://en.wikipedia.org/wiki/Valencian_Community
- https://en.wikipedia.org/wiki/Aragon
All of them share the coat of arms of the crown of Aragon: https://en.wikipedia.org/wiki/Coat_of_arms_of_the_Crown_of_A... . Thus using the "four red pallets on a gold background" represents all the speakers in different European countries.