s/a tan bajo nivel y pueden no entender/a tan bajo nivel y no pueden entender/;

I disagree on this one. What I meant is "it's possible that they don't understand", not "they can't understand". Original says "may not understand".

s/este pero alguna de las cosas/éste pero algunas de las cosas/; # no estoy seguro del acento

I'm not sure about the written accent either, but I'll leave it as it is now because there's no risk of confusion.

s/should produce 'hello/debería producir 'hello/;

Hmm, I missed those. I'm fixing it now.

perhaps nybble needs an explanation

It is briefly explained just under the third table.

Thank you for the input.