Fcitx(Free Chinese Input Toy for X) is a collection of Simplified
Chinese input methods for Linux. It supports Pinyin, QuWei and
Table-based input methods.

If you have installed Gtk3 or OpenCC, you may run as below to make
fcitx support them:
$ GTK3=On OPENCC=On ./fcitx.SlackBuild

You may need 'fcitx-configtool', a GUI tool for configuring fcitx.

This requires icu4c.
