I would just roll my eyes at SE writers/developers, is how I'd handle it. I am not sure honestly, to me following lore in the case that they do state that there is one common language would be a step down from taking into account various languages.
As for the specifics you mentioned in your spoiler:
Personally, I've not seen anything to compelling to switch me over to the "one language" camp, but that said I am not even sure if I recall exact cases (if there are any) where it /did/ make clear that Garleans have their own language. So, it's up in the air for now - but since I am a linguistics nerd I prefer the multiple languages.
As for the specifics you mentioned in your spoiler:
Personally, I've not seen anything to compelling to switch me over to the "one language" camp, but that said I am not even sure if I recall exact cases (if there are any) where it /did/ make clear that Garleans have their own language. So, it's up in the air for now - but since I am a linguistics nerd I prefer the multiple languages.
I’m the bullies you hate, that you became.