app/assets/javascripts/timeago/jquery.timeago.ja.js
// Japanese
jQuery.timeago.settings.strings["ja"] = {
prefixAgo: "",
prefixFromNow: "今より",
suffixAgo: "前",
suffixFromNow: "後",
seconds: "数秒",
minute: "約一分",
minutes: "%d分",
hour: "約1時間",
hours: "約%d時間",
day: "1日",
days: "%d日間ほど",
month: "約1ヶ月",
months: "%dヶ月ほど",
year: "約1年間",
years: "%d年間",
wordSeparator: ""
};