Превод - Гръцки-Английски - ...υπάρχουν οι τοίχοι οι θεόρατοι

Two small corrections:

from nowhere --> from anywhere
not even those --> not even from those

the word πουθενα means nowhere, anywhere is καπου.
I agree with the correction "not even from those", I do agree that the word "from" needs to be added!

Yes, but we have two negatives here... "can't", "nowhere"...

"Anywhere" is translated and as "πουθενά" when there is a negative in the sentence ( "can't" ).

My question as a non native speaker: Is using these 2 negatives together acceptable by a native in everyday talking?

CC: kafetzou

Yes, I agree we do have two negatives here just like the way the sentence was written in Greek: και δεν 'γεμίζεις' από πουθενά.
I am not doing a grammatical improvement to the text, I am translating it. So, if there were 2 negatives in the original text, I do not see any reason for not using be 2 negatives also in the translation. And yes, 2 negatives are often used in everyday language in English just like in Greek.
Also, I feel that we are wasting time and energy on a trivial matter discussing whether it should be nowhere or anywhere, since both words fit the meaning just as you mentioned. If you want to use anywhere instead of nowhere go ahead. No problem.

No. That's why I posted the correction. "not ... anywhere" is correct. "not ... nowhere" is incorrect.

Aspiebrain, you write like a native speaker of English, but double negatives are incorrect in English. You should know that.

P.S. Somewhere is καπου.