SCIM stands for 'Smart Common Input Method'. The SCIM engine can act as an input method for any language, including complex languages such as Chinese. It is easy to use SCIM tables to create a custom keyboard.
SCIM is a useful alternative to xkb for switching between keyboard layouts. SCIM provides some functions that xkb does not. I personally use it to type ancient Greek, pointed Hebrew, and Chinese.
SCIM is no more difficult to setup in Xfce than in GNOME or KDE. The easiest, user-level way to set up SCIM is to edit the .Xsession file:
LANG=en_US.UTF-8 export LANG XMODIFIERS="@im=SCIM" export XMODIFIERS GTK_IM_MODULE="scim" export GTK_IM_MODULE scim -d& startxfce4
Set “LANG” to your own local language, of course. SCIM should work as long as the locale is UTF-8. After doing this, SCIM will work in Xfce by default.