https://inkscape.org/forums/beyond/not- ... own/#c5602I fix the problem!
And it's not what everyone repeats again and again!
The problem is that windows has a bug (or is it a feature?) with the registry. If you install a font correctly - and this is to copy it manually to c:/windows/font - the necessary registry entries eventually are not created (correctly). And this will be a problem for Inkscape - because other programs show the fonts.
So remove all fonts from the windows-dir to a temp-dir (the system fonts can not be moved)
donwload FontReg
http://code.kliu.org/misc/fontreg/ unzip FontReg and move the Fontreg.exe to the temp font-dir
start command line/shell: WIN+R and "cmd"
change to temp font-dir
fontreg /copy
all fonts will be installed new and the problem is fixed.