Hanging punctuation is “a way of typesetting punctuation marks and bullet points, most commonly quotation marks and hyphens, so that they do not disrupt the ‘flow’ of a body of text or ‘break’ the margin of alignment.” (Wikipedia says it better than me ;) )
I cannot find any good translation for this concept in French. Anyone with formal typography education around here? :)
Try Linguee when you want to translate technical phrases. It's a database of bilingual texts in various language pairs, including French and English.
There is one hit for hanging punctuation: “ponctuation hors justification”, found in a Quark, Inc. brochure. I don't have an official reference to offer, but several manufacturers of typographical software (Quark, Adobe) have used the term, as have books about CSS, so I would guess that it is indeed the standard translation.
The phrase “ponctuation hors justification” gets a decent number of hits on Google, unlike “ponctuation dans la marge” (which has a single relevant hit), “ponctuation pendante” (which isn't much better, in spite of its obviousness as a literal translation), or “ponctuation suspendue” (most of the hits are unrelated).
The question was asked in passing on the typographie mailing list, with no conclusive answer.
Une discussion sur la liste typo a utilisé ponctuation dans la marge, ponctuation pendante et même « hanging punctuation ». J'ai donc l'impression qu'il n'y a pas (au moins qu'il n'y avait pas à l'époque) de traduction consacrée. La « justification optique » aussi présente dans cette discussion est plus large, la ponctuation pendante est un moyen d'y arriver.
