https://bugzilla.redhat.com/show_bug.cgi?id=1138384
--- Comment #1 from Jens Petersen petersen@redhat.com --- I really blame rpmbuild for still using LANG=C by default... :)
Anyway as I commented in bug 1136297 you can workaround this by setting LANG=en_US.utf8 before %cabal_lib_build. Like this:
%build LANG=en_US.utf8 %ghc_lib_build