Okay, so I may or may not write books where the characters are in theory speaking in a language other than the one I'm writing in. So I may (or may not) know a little about this.
I get what you're saying, absolutely, but there's a reason that Sel (and writers like him) have to do it the way they do.
Wordplay famously doesn't translate -- especially across languages that don't share much (or any) vocabulary. And since certain characters kind of have to use puns and all the rest of it, you have to decide that you're going to play your silly games in the language you're writing in. Then you hope that the reader understands that what they're reading is a suggestion of how the characters are talking, rather than a literal record of what they're actually saying. It's why machine translation will always suck, especially around any kind of double entendre or other wordplay.
Because no one wants translation footnotes in their novels. Or VNs, for that matter.
The only other options are a) to have the characters making witty/snarky remarks in a language where those remarks make no sense or b) have them speak only in concrete, humorless language where translation won't ever be a problem. (BTW, such language really doesn't exist.)
I mean, in my writing (which is also set in another time period), I'm always careful not to have references to anachronisms or things the characters have no way of knowing about. Sometimes it's hard. Rather than use the obscure time units of the time and place my books are set in, I found I'd started to measure time in breaths and heartbeats and such, for example. I try to write from inside my characters' heads, even if the language I'm using to write down their thoughts and perceptions isn't the one they think in.
Mostly, I trust that the readers will go along with it. I get that in this case you found you couldn't. But I mostly find that I'm happy going along with Sel when he makes a joke that only really hits in Texas.
Does that make sense?