有2种方法解决,2选一

1，用 groff-1.18.1 就可以直接支持UTF－8
所以可以不用这个groff-utf8，那么只要将 groff-1.19 mask了，降级到1.18.
如
echo ">=sys-apps/groff-1.19.2" >/etc/portage/package.mask
emerge groff

2，如果不想降级 groff，那么1.19在处理utf8上有bug这时就可以安装这个groff-utf8了

# emerge groff-utf8

按照安装完的提示修改/etc/man.conf的NROFF 变量

 * Messages for package app-text/groff-utf8-0:

 * Sample usage:
 * $ groff-utf8 -Tutf8 -mandoc find.vi.1 | less
 * $ groff-utf8 -Thtml -mandoc find.vi.1 > find.html; mozilla find.html
 *
 * You can also modify the TROFF/NROFF settings in your /etc/man.conf
 * to make it use groff-utf8 instead of groff.
 * For example:
 * NROFF       /usr/bin/groff-utf8 -Tutf8 -c -mandoc