icu4c-opt (International Components for Unicode)

The International Components for Unicode (ICU) libraries provide
robust and full-featured  Unicode services on a  wide variety of
platforms.  This version is installed  to /opt/ to provide newer
ICU libraries on Slackware stable.

This version of the library is  installed to /opt, to help build
software that requires a newer version than the one available in
the Slackware base system.  To build against this version of the
library,  you have  to  configure your  build system's  includes
search path to find `*.h' files in /opt/icu/usr/include/unicode,
and  set  RPATH to  link  against  the `*.so'  shared  libraries
installed in /opt/icu/usr/lib64.