What's nonsensical and what is not is subjective. Different people assume different things about everything that's not explicit. That's why we are having this "this" vs "next" discussion in the first place.

Connecting "next" with a German translation of "nähest" ("closest") is just as nonsensical.

Yes, but "this" doesn't imply timing either way.

So if on Saturday you said "our dinner reservations are next Friday, not this Friday", that could mean

— "we didn't forgot to go yesterday, we have dinner in 6 days time" (where 'this Friday' is 'Friday of this week') or could mean

— "we're not going to dinner in 6 days time, we're going to dinner in 13 days time" (where 'this Friday' is 'the Friday in this rolling block of 7 days' and 'next Friday' is the one after that).

Sounds very contrived, but people do use it in both ways and neither really has a dominance unfortunately.