OK, this may not be of much help, but I just converted GenR102.TTF to pfb via fontforge, and now the font correctly picks up the dcroat glyph. I mus admit I had similar situations in the past where simply regenerating the font would solve mysterious problems, so I shrugged my shoulders and did what a man must do. I think the new Gentium license allows for this conversion, and the LaTeX people will be distributing pfbs anyway, so why not convert to pfb (which is easier for TeX to use anyway?)
Hi Thomas, You're completely right ! Just tried with PFB (converted by fontforge) and it works :)
Package Gentium (PFB converted by fontforge) with qx,t5,texnansi, ec : http://people.vnoss.org/~vnpenguin/pub/context/fonts/Gentium102-context.tgz Tested ok with T5. -- http://vnoss.org Vietnamese Open Source Software Community