"... this falsehood perpetuated on the big screen in Quentin Tarantino's Django Unchained where the eponymous character spells his name, adding 'the D is silent'."
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"The D is not silent, it's very much pronounced."
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"... Tarantino's film teaches the correct pronunciation ... it is incorrect to say 'the D is silent'."
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"But in French, /dʒ/ can be written 'dj' because the 'j' alone is just /ʒ/."
OK, if the "d" is not silent, don't you mean that /dʒ/ must be written "dj"?
Why not just say that, in English, "j" as in "James" has the tongue touching the roof of the mouth, so it always sounds a little like a "d", but in French it doesn't?