See attached screenshot!
Created attachment 126177 [details] gsview screenshot
Please, report this upstream; not a Gentoo issue (plus will probably remain broken while this uses the crappy gtk-1.2).
It seems to be a problem with the de_DE.utf8 locales when setting the locale to de_DE the entries are displayed properly. So if upstream will not switch to gtk-2 this problem will probably remain. I have seen this with other gtk-1 GUI's too, didn`t thought of it although the GUI clearly looks like a gtk-1 one. Maybe it is the wrong place to ask for, but is there a way to modify the gsview.desktop file to use another locale.