fcitx5-gtk provides the GTK IM modules and libraries for fcitx5.

If you enable GObject Introspection (via the ENABLE_GIR CMake
variable), make install will install some files to the system's GIR
directories regardless of what CMAKE_INSTALL_PREFIX is set to.

If you have installed it to a custom prefix, you'll need to update the
GTK input method module cache. This is done by invoking
gtk-query-immodules-3.0 (or gtk-query-immodules-3.0 for GTK 2) and
setting GTK_PATH to point at fcitx5-gtk's GTK library install path
beforehand. For example:

    GTK_PATH=/your/install/path/lib/gtk-3.0 gtk-query-immodules-3.0 \
        --update-cache