Did you read the article? It's merely "partial" for Danish versus Norwegian and Swedish, while "very high" for Galician and Portugese. So no, they wouldn't be.
Yeah, I have read the article and 85% or "very high" is "merely partial" as well. The reason those three are only partial is that they're on a continuum such that Norwegians understand both, but Danes and Swedes have a harder time understanding each other. You see similar gradients in Iberia as well. Plus, that's based on the modern languages. The split started around the 1200's and, even till the 20th century, Danish was basically the written standard for Norwegian.
The cultures composing the Langues d'oïl (in-game Norman, Francien, Burgundian) and Langue d'Oc (i.e. Occitan) (in-game Occitan, Gascon, Aquitanian) were all mutually intelligible as well, should they be combined?
Not really - You're the one proposing the change, yet you've only provided a single citation based a one aspect of culture i.e. language. I frankly don't care one way or the other, but you haven't provided enough evidence they should be the same. The devs likely have better reasoning/sources for the split, but I don't have the time to waste looking crap up.
I get that your original post was "asking" for differences (i.e. sources) to justify the split, but your responses have been dismissive. If you were really "just interested" and wanted sources for further research, "citation needed" is a pretty rude response. Truth is, at least in English, it's hard to find primary sources
justifying either splitting or combining, but just the fact that "Galician" is different enough to mention, referenced often, and that they developed under different sovereigns, is enough for me to support keeping them separate.
Sure, the cultural designations are somewhat fuzzy and there's no clear rule for what's split and what's not. Language, by itself, isn't enough. That's like saying American, English, & Australian are the same; or Mexican, Argentinian, Chilean, Filipino, and Spanish are the same. And yes, I understand all these developed outside the game's timeframe, but that's irrelevant because they're all counter-examples to the your claim that "Their languages are highly similar, why aren't they the same culture."