Once I installed fctix-mozc package and make ~/.xprofile following the wiki. Then I noticed I can enter Japanese inside only shell console, but can’t in other applications like firefox. The problem is that I only installed one package of fctix-im package group. It turned work fine after I installed all input method packages that the fctix-im includes(fcitx-gtk2, fcitx-gtk3, fcitx-qt4 and fcitx-qt5):D