fk lese(&selbst, schlsl: Zeichenkette) -> Ergebnis<Möglichkeit<&Zeichenkette>, Zeichenkette> {
            wenn lass Etwas(wöbu) = gefährlich { WÖRTERBUCH.als_ref() } {
                Gut(wöbu.hole(&schlsl))
            } anderenfalls {
                Fehler("Holt das Wörterbuch".hinein())
            }
        }
isn't the idea behind programming "languages", that they are sentences readable to both humans and the compiler?

This absolutely is not readable to me. But woerterbuch and schluessel should of course not be abbreviated, for legibility.

If German was seriously used in programming languages, I'd hope for some better and shorter terms. Some here might be intentionally too literal translations anyway. "Let" is from mathematics, it's called "Sei" in German. "Sei x = 5". "Anderenfalls" could be "sonst". "Zeichenkette" is just too long and would require some thinking or a historical accident to find a shorter term.

Ready surprisingly nice to me anyway.

I would use "sei" instead of "lass" for "let" to be more in line with notation in mathematical proofs.