Fcitx [ˈfaɪtɪks] is an input method framework with extension support. Currently it supports Linux and Unix systems like freebsd. It has three built-in Input Method Engine, Pinyin, QuWei and Table-based input methods.

Fcitx tries to provide a native feeling under all desktop as well as a light weight core. You can easily customize it to fit your requirements.

To install it, pull up a terminal and install the japanese fcitx input module and a japanese font of your choice, i picked noto-font-cjk:

yay -S fcitx5-kkc

Configure fcitx-configtool so you can switch between your input languages (if you use dwm it will open up a text file):

In case you have dwm, you need to uncommend a specific line, it should now look something like:

[Hotkeys]
TriggerKey=CTRL_SPACE

See locale for details.

Locales are used to correctly display regional or language/locale-specific standards. To ensure the Japanese locale is enabled, confirm that ja_JP.utf8 is in the output of:

$ locale -a

To enable the Japanese locale, uncomment ja_JP.utf8 in /etc/locale.gen:

/etc/locale.gen
-------------------
#ja_JP.EUC-JP EUC-JP
ja_JP.UTF-8 UTF-8
#ka_GE.UTF-8 UTF-8

Afterwards, regenerate your locale:

# locale-gen

After the installation you need to configure fcitx in your .xprofile, which means your system enviroment so that your system accepts fcitx as standard input:

export GTK_IM_MODULE=fcitx 
export QT_IM_MODULE=fcitx 
export XMODIFIERS=@im=fcitx

Reboot your system so that it takes effect.