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.