Fcitx5

Fcitx5 is a lightweight input method framework with addon support.

Setup

nixos-unstable

The following is a simple NixOS configuration that sets up fcitx5 on nixos-unstable:

 i18n.inputMethod = {
   type = "fcitx5";
   enable = true;
   fcitx5.addons = with pkgs; [
     fcitx5-mozc
     fcitx5-gtk
   ];
 };

nixos-24.05 and before

The i18n.inputMethod.enabled option will be removed in favor of .type and .enable (see above).

Until then, a simple example for Simplified Chinese:

 { config, pkgs, ... }:
 {
   i18n.inputMethod = {
     enabled = "fcitx5";
     waylandFrontend = true;
     fcitx5.addons = with pkgs; [
       fcitx5-gtk             # alternatively, kdePackages.fcitx5-qt
       fcitx5-chinese-addons  # table input method support
       fcitx5-nord            # a color theme
     ];
   };
 }

For Traditional Chinese, one can use the RIME Input Method Engine:

 { config, pkgs, ... }:
 {
   i18n.inputMethod = {
     enabled = "fcitx5";
     waylandFrontend = true;
     fcitx5.addons = with pkgs; [
       rime-data
       fcitx5-gtk
       fcitx5-rime
     ];
   };
 }

The i18n.inputMethod.enabled option provides alternative input methods to fcitx5, but these can also be enabled as fcitx5 addons.

Addons include:

__input methods__: fcitx5-rime, fcitx5-skk, fcitx5-mozc, fcitx5-openbangla-keyboard, fcitx5-bamboo
__themes__: fcitx5-nord, fcitx5-rose-pine, fcitx5-material-color
Zhuyin/Bopomofo input via fcitx5-chewing

Notably, NixOS sets session variables that are required for fcitx5.

Currently, home-manager does not have fcitx5 settings.

So it may be necessary to update settings in ~/.config/fcitx5, e.g.

 # ~/.config/fcitx5/conf/classicui.conf
 Theme=Nord-Dark
 Font="Meslo 20"

If you run Hyprland and want the GUI to appear on start:

 # ~/.config/hypr/hyprland.conf
 windowrule = pseudo, fcitx
 exec-once=fcitx5 -d -r
 exec-once=fcitx5-remote -r

Troubleshooting

Add-ons Not Detected

Installing fcitx5 using environment.systemPackages can interfere with add-on detection. Make sure to only add fcitx5 to your config as shown in Setup.

Fcitx5 failing to load IME module (claims "使用不可" (unusable))

Another possibility is that you are calling ${pkgs.fcitx5}/bin/fcitx5 instead of the patched fcitx5-with-addons (/run/current-system/sw/bin/fcitx5). For example in Hyprland:

 # ~/.config/hypr/hyprland.conf
 exec-once=fcitx5 -d # not ${pkgs.fcitx5}/bin/fcitx5 !

Fcitx5 Doesn't Start When Using WM

As of NixOS 23.11 i18n.inputMethod.enabled no longer creates systemd services for fcitx5. Instead it relies on XDG autostart files. If using a Window Manager (WM), such as Sway, you may need to add services.xserver.desktopManager.runXdgAutostartIfNone to your NixOS configuration.

See the NixOS 23.11 Release Notes for more information.

Using Wayland

Set boolean i18n.inputMethod.fcitx5.waylandFrontend to true to suppress warnings about environment variables.

Simplified Pinyin layout does not appear

When running fcitx5-configtool, the Simplified Chinese layouts don't appear if you write "Chinese", but they appear if you write "cn": Here a "Pinyin" option occurs under "简体中文":

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