Recent fontconfig (2.13.0 and after) calls setlocale (LC_ALL, "") in its init code. This stomps on our value of LC_NUMERIC, which needs to be "C", in order for #'read to handle floats correctly, where the decimal separator is always the character ?. . This means that, e.g. on a GTK build in a German locale the mouse wheel doesn’t work, because mouse-wheel-inhibit-click-time is 0.0 instead of 0.35. We’ve encountered similar problems before, with the X11 code (see comments in init_x_locale()) and the GTK code (see Fgtk_init()). The right longer-term answer, and something that would fix the asymmetry that non-ASCII digits are recognised in the Lisp reader as reflecting integers but not floats, is for us to add a copy of David Gay’s dtoa.c to our tree, extended to use our radix table as appropriate. -- ‘As I sat looking up at the Guinness ad, I could never figure out / How your man stayed up on the surfboard after forty pints of stout’ (C. Moore)