First question: Is this sentence supposed to be humorous ? To me it makes no sense, is it intended in the movie or does the sentence seem logical to you ?
In some languages, j is pronounced /ʒ/ (like in "lesion"), so adding a 'd' makes the sound /dʒ/. That's why the name of Django Reinhardt is written like that, in his language, if there was no 'D' or if the 'D' was silent, his name would be pronounced "ʒango". But how does it make sense for the 'D' of "Django" to be silent ? It would have be pronounced "Jango" anyway.
Would it be pronounced "duh-jango" if the 'D' wasn't silent ? I know it's just to give style but the sentence wouldn't be relevant
I read this before writing my question, it didn't help.