Galician gets official EU language status, but a regional language in another EU member that has official status at a national level doesn’t.

At least Catalan (not sure about Galician or Basque) is a bit different from other regional languages. The education system in Spain is federated to regions, so children in Catalunya speak Catalan most of the time, Castillano/Spanish being a second language. In comparison, the French education system is monolithic, so all French children learn in French. There are a few schools who speak Breton or Catalan, but those are really minorities compared to Spain. Even from an official perspective, Breton or Catalan are not official languages of their regions in France.

EDIT: Maybe Spain could just commit to internally providing and funding Catalan, Basque, and Galician translations of EU official documents, as that wouldn’t require sign-off from other EU members.

That probably wouldn’t be enough. Catalan, Basque and Galician speakers also ask for the right of their representatives to speak their languages at the European Parliament and other instances, which requires translators from those languages to all of the other languages.

Also, about the cost, the EU pays for translators for Irish, which has less than 2 millions L2 speakers (https://en.wikipedia.org/wiki/Irish_language), Latvian with 1.5 millions speakers (https://en.wikipedia.org/wiki/Latvian_language), Maltese with less than 600,000 speakers (https://en.wikipedia.org/wiki/Maltese_language), why wouldn’t the EU pay for Catalan, which has 4 millions of L1 speakers, and 5 millions of L2 speakers (https://en.wikipedia.org/wiki/Catalan_language)?

If the argument is “yes, but they are their own country”, then that’s just going to give ammunition to the Catalan independentists.