Please read http://fcitx-im.org for further help.

All source in fcitx are released under GPLv2+, but for all addon running inside
Fcitx, you don't need to obey GPLv2+. GPLv2+ will only protect the modification
and redistribution for code inside fcitx, which means you can use any license for
addon running in Fcitx even if you are using fcitx, fcitx-config, fcitx-utils.

And fcitx also provides some way to do inter-process-communication (IPC), using
these interfaces also don't bring any limitation to your code.