Input Methods
Input methods are an operating system component that allows any data, such 
  as keyboard strokes or mouse movements, to be received as input. In this way 
  users can enter characters and symbols not found on their input devices. Using 
  an input method is obligatory for any language that has more graphemes than 
  there are keys on the keyboard.
The following input methods are available in NixOS:
  IBus: The intelligent input bus.
  Fcitx: A customizable lightweight input 
      method.
  Nabi: A Korean input method based on XIM.
  Uim: The universal input method, is a library with a XIM 
      bridge.
IBus
IBus is an Intelligent Input Bus. It provides full featured and user 
  friendly input method user interface.
The following snippet can be used to configure IBus:
i18n.inputMethod = {
  enabled = "ibus";
  ibus.engines = with pkgs.ibus-engines; [ anthy hangul mozc ];
};
i18n.inputMethod.ibus.engines is optional and can be 
  used to add extra IBus engines.
Available extra IBus engines are:
  Anthy (ibus-engines.anthy): Anthy is a 
      system for Japanese input method. It converts Hiragana text to Kana Kanji 
      mixed text.
  Hangul (ibus-engines.hangul): Korean input 
      method.
  m17n (ibus-engines.m17n): m17n is an input 
      method that uses input methods and corresponding icons in the m17n 
      database.
  mozc (ibus-engines.mozc): A Japanese input 
      method from Google.
  Table (ibus-engines.table): An input method 
      that load tables of input methods.
  table-others (ibus-engines.table-others): 
      Various table-based input methods.
Fcitx
Fcitx is an input method framework with extension support. It has three 
  built-in Input Method Engine, Pinyin, QuWei and Table-based input 
  methods.
The following snippet can be used to configure Fcitx:
i18n.inputMethod = {
  enabled = "fcitx";
  fcitx.engines = with pkgs.fcitx-engines; [ mozc hangul m17n ];
};
i18n.inputMethod.fcitx.engines is optional and can be 
  used to add extra Fcitx engines.
Available extra Fcitx engines are:
  Anthy (fcitx-engines.anthy): Anthy is a 
      system for Japanese input method. It converts Hiragana text to Kana Kanji 
      mixed text.
  Chewing (fcitx-engines.chewing): Chewing is 
      an intelligent Zhuyin input method. It is one of the most popular input 
      methods among Traditional Chinese Unix users.
  Hangul (fcitx-engines.hangul): Korean input 
      method.
  Unikey (fcitx-engines.unikey): Vietnamese input 
      method.
  m17n (fcitx-engines.m17n): m17n is an input 
      method that uses input methods and corresponding icons in the m17n 
      database.
  mozc (fcitx-engines.mozc): A Japanese input 
      method from Google.
  table-others (fcitx-engines.table-others): 
      Various table-based input methods.
Nabi
Nabi is an easy to use Korean X input method. It allows you to enter 
  phonetic Korean characters (hangul) and pictographic Korean characters 
  (hanja).
The following snippet can be used to configure Nabi:
i18n.inputMethod = {
  enabled = "nabi";
};
Uim
Uim (short for "universal input method") is a multilingual input method 
  framework. Applications can use it through so-called bridges.
The following snippet can be used to configure uim:
i18n.inputMethod = {
  enabled = "uim";
};
Note: The i18n.inputMethod.uim.toolbar option can be 
  used to choose uim toolbar.