Fortean Times recently that the last fluent writer and speaker of nushu died in autumn 2004.
This language - nushu means "women's writing" - was unique in that it was invented and used only by women in an area of Hunan, a province in China, who were denied the education available only to boys, and so learned from each other (there seem to have been links between the language and an interesting tradition of "sworn sisters" too). They could use nushu to communicate secretly in a way that men would not be able to follow (hey, I know some men say they can't understand women's conversations even now, but...!).
I've not heard of any other language which is specific to a gender, rather than an ethnic group. Some scholars fortunately recorded as much as they could from the few surviving users, but it seems to me particularly tragic when, with the death of one person, an entire once-living, rich and unique language also dies.
This page seems to be the most comprehensive, though quite academic, collection of articles etc. on the Web on nushu, and includes links to items which show the fluid pictograms used in nushu, such as this paper. A more accessible, readable article on nushu is here.
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