The English equivalent of the Arabic: “Something is innocent of you”

You wouldn’t know democracy ... if it stared you in the face!

stare in the face idiom (The Free Dictionary)

When someone says this of another, they are employing hyperbole and sarcasm, since something that is staring you in the face ... is right before your eyes and plainly evident, so this idiom means, in effect, you not only are NOT a custodian of democracy, you don’t even know what a democracy is! So the Arabic phrase "innocent of you" is a bit more ... understated.

The word "innocent" has this same meaning in English, i.e., free from or devoid of. The OED gives the example sentence "The sermon ... was innocent of meaning."

The use has a somewhat mocking sense. In your examples of "innocent of you," as though involving you would be a guilty act.

A: I am the custodian of democracy.
B: Democracy? You don't even know the meaning of the word.

B is saying that A doesn't know what ‘democracy’ is; he might be implying that A is a hypocrite, a perfect idiot, or totally ignorant.