Sanderson uses the hypothetical translator as a writing construct, not because there is a canon In-Universe Author.
Questioner: Hang on a moment.... I always assumed that the translation effect from in-world language to English (or other Earth languages that allowed us to read the books) was more of a passive thing, almost like we are 'Connecting' to the stories which enables us to read the words that make sense to us.
Are you saying here that the process is actually by design? That someone (from the sounds of it Khriss) is somehow actively translating the events of the books and that's why we read them in our native language? Is this something that has been discussed before and I missed it?
Brandon Sanderson: I've always imagined a hypothetical translator into English, more as a writing construct (to explain certain things and the way I do things) than anything else. I wouldn't consider it canon, in that there is no Earth in the cosmere, but it's how I frame the process for myself. It's how I explain to myself that certain metaphors work and the like.
Arcanum | Coppermind
He goes into greater depth about the process in this quote:
Questioner: So, when there's wordplay in The Stormlight Archive, we know they aren't speaking English, so are you to assume that that is a translation of the...
Brandon Sanderson: This is what Tolkein said, and I always rely upon this. You're reading the book in translation, and the person translating it is going to try to use the closest in feel, but to also make it translate to English. So even when they use idioms and things like that, sometimes they translate and the translator can drop them in. Sometimes they just don't translate, so the translator comes up with something that works in English... It gets you a lot of loopholes, like if you accidentally call something an ottoman and people are like, "But there's not an Ottoman Empire in this fantasy world!" But you're like, "Yeah, all words work that way." It's in translation. This is why when you read something like Allomancy, and they're like, "Well, it's got Latin roots, right?" Yeah... it's just the roots in their language would be something old Terris, and the easiest way to convey that feeling is to use something that's got-- you know. Stuff like that.
Arcanum | Coppermind
Obviously there are some In-Universe texts that are "translated" directly, in whole or in part, outside the story. The Ars Arcanum, Alendi's Journal, Kwaan's Inscription, The Words of Founding, Death Rattles, and The Diagram to name a few. But these are exceptions, not the rule.