This template marks the kanji segment as being in Japanese kanji and/or kana, which helps user agents (web browsers and so on) to display it correctly. It also applies the t_nihongo_kanji CSS class.
English: Optional. The word as translated into English. Note that this will sometimes be the actual Japanese word due to it being adopted into English.
kanji/kana: Required. The word in Japanese kanji and/or kana, the logographic writing system.
rōmaji: Optional. The word in Japanese rōmaji, the Romanized syllabic writing system used for foreign words. Also known as a "transliteration".
extra: Optional. Can also be expressed as a named parameter, extra=
extra2: Optional. Can also be expressed as a named parameter, extra2=. It is only useful in ";" definitions (extra2 will be displayed without bold, whereas text following the template will get the bold).