The installation determines the path "/usr/lib/locale" for installing the locale files. AFAIK, that should be /usr/share/locale. In my gentoo, Windowmaker was the only one who installed locales to /usr/lib/locale, so I think it's a bug in the ebuild. I hope I'll be able to send a patch in a while.
Created attachment 66859 [details, diff] Solution for installing the locales to /usr/share/locale/ Here is the patch... I've tried it. In the patch there aren't the changes to the Manifest.
Finally fixed in windowmaker-0.92.0-r4 (currently in the gnustep overlay, soon in portage), thanks!