discourse/app/assets/javascripts/locales/i18n.js

// Instantiate the object
var I18n = I18n || {};

// Set default locale to english
I18n.defaultLocale = "en";

// Set default pluralization rule
I18n.pluralizationRules = {
  en: function(n) {
    return n === 0 ? ["zero", "none", "other"] : n === 1 ? "one" : "other";
  }
};

// Set current locale to null
I18n.locale = null;
I18n.fallbackLocale = null;

// Set the placeholder format. Accepts `{{placeholder}}` and `%{placeholder}`.
I18n.PLACEHOLDER = /(?:\{\{|%\{)(.*?)(?:\}\}?)/gm;

I18n.SEPARATOR = ".";

I18n.noFallbacks = false;

I18n.isValidNode = function(obj, node, undefined) {
  return obj[node] !== null && obj[node] !== undefined;
};

I18n.lookup = function(scope, options) {
  options = options || {};

  var translations = this.prepareOptions(I18n.translations),
    locale = options.locale || I18n.currentLocale(),
    messages = translations[locale] || {},
    currentScope;

  options = this.prepareOptions(options);

  if (typeof scope === "object") {
    scope = scope.join(this.SEPARATOR);
  }

  if (options.scope) {
    scope = options.scope.toString() + this.SEPARATOR + scope;
  }

  var originalScope = scope;
  scope = scope.split(this.SEPARATOR);

  if (scope.length > 0 && scope[0] !== "js") {
    scope.unshift("js");
  }

  while (messages && scope.length > 0) {
    currentScope = scope.shift();
    messages = messages[currentScope];
  }

  if (messages === undefined && this.extras && this.extras[locale]) {
    messages = this.extras[locale];
    scope = originalScope.split(this.SEPARATOR);

    while (messages && scope.length > 0) {
      currentScope = scope.shift();
      messages = messages[currentScope];
    }
  }

  if (messages === undefined) {
    messages = options.defaultValue;
  }

  return messages;
};

// Merge several hash options, checking if value is set before
// overwriting any value. The precedence is from left to right.
//
//   I18n.prepareOptions({name: "John Doe"}, {name: "Mary Doe", role: "user"});
//   #=> {name: "John Doe", role: "user"}
//
I18n.prepareOptions = function() {
  var options = {},
    opts,
    count = arguments.length;

  for (var i = 0; i < count; i++) {
    opts = arguments[i];

    if (!opts) {
      continue;
    }

    for (var key in opts) {
      if (!this.isValidNode(options, key)) {
        options[key] = opts[key];
      }
    }
  }

  return options;
};

I18n.interpolate = function(message, options) {
  options = this.prepareOptions(options);

  var matches = message.match(this.PLACEHOLDER),
    placeholder,
    value,
    name;

  if (!matches) {
    return message;
  }

  for (var i = 0; (placeholder = matches[i]); i++) {
    name = placeholder.replace(this.PLACEHOLDER, "$1");

    if (typeof options[name] === "string") {
      // The dollar sign (`$`) is a special replace pattern, and `$&` inserts
      // the matched string. Thus dollars signs need to be escaped with the
      // special pattern `$$`, which inserts a single `$`.
      // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace#Specifying_a_string_as_a_parameter
      value = options[name].replace(/\$/g, "$$$$");
    } else {
      value = options[name];
    }

    if (!this.isValidNode(options, name)) {
      value = "[missing " + placeholder + " value]";
    }

    var regex = new RegExp(
      placeholder.replace(/\{/gm, "\\{").replace(/\}/gm, "\\}")
    );
    message = message.replace(regex, value);
  }

  return message;
};

I18n.translate = function(scope, options) {
  options = this.prepareOptions(options);
  options.needsPluralization = typeof options.count === "number";
  options.ignoreMissing = !this.noFallbacks;

  var translation = this.findTranslation(scope, options);

  if (!this.noFallbacks) {
    if (!translation && this.fallbackLocale) {
      options.locale = this.fallbackLocale;
      translation = this.findTranslation(scope, options);
    }

    options.ignoreMissing = false;

    if (!translation && this.currentLocale() !== this.defaultLocale) {
      options.locale = this.defaultLocale;
      translation = this.findTranslation(scope, options);
    }

    if (!translation && this.currentLocale() !== "en") {
      options.locale = "en";
      translation = this.findTranslation(scope, options);
    }
  }

  try {
    return this.interpolate(translation, options);
  } catch (error) {
    return this.missingTranslation(scope);
  }
};

I18n.findTranslation = function(scope, options) {
  var translation = this.lookup(scope, options);

  if (translation && options.needsPluralization) {
    translation = this.pluralize(translation, scope, options);
  }

  return translation;
};

I18n.toNumber = function(number, options) {
  options = this.prepareOptions(options, this.lookup("number.format"), {
    precision: 3,
    separator: this.SEPARATOR,
    delimiter: ",",
    strip_insignificant_zeros: false
  });

  var negative = number < 0,
    string = Math.abs(number)
      .toFixed(options.precision)
      .toString(),
    parts = string.split(this.SEPARATOR),
    buffer = [],
    formattedNumber;

  number = parts[0];

  while (number.length > 0) {
    buffer.unshift(number.substr(Math.max(0, number.length - 3), 3));
    number = number.substr(0, number.length - 3);
  }

  formattedNumber = buffer.join(options.delimiter);

  if (options.precision > 0) {
    formattedNumber += options.separator + parts[1];
  }

  if (negative) {
    formattedNumber = "-" + formattedNumber;
  }

  if (options.strip_insignificant_zeros) {
    var regex = {
      separator: new RegExp(options.separator.replace(/\./, "\\.") + "$"),
      zeros: /0+$/
    };

    formattedNumber = formattedNumber
      .replace(regex.zeros, "")
      .replace(regex.separator, "");
  }

  return formattedNumber;
};

I18n.toHumanSize = function(number, options) {
  var kb = 1024,
    size = number,
    iterations = 0,
    unit,
    precision;

  while (size >= kb && iterations < 4) {
    size = size / kb;
    iterations += 1;
  }

  if (iterations === 0) {
    unit = this.t("number.human.storage_units.units.byte", { count: size });
    precision = 0;
  } else {
    unit = this.t(
      "number.human.storage_units.units." +
        [null, "kb", "mb", "gb", "tb"][iterations]
    );
    precision = size - Math.floor(size) === 0 ? 0 : 1;
  }

  options = this.prepareOptions(options, {
    precision: precision,
    format: this.t("number.human.storage_units.format"),
    delimiter: ""
  });

  number = this.toNumber(size, options);
  number = options.format.replace("%u", unit).replace("%n", number);

  return number;
};

I18n.pluralizer = function(locale) {
  var pluralizer = this.pluralizationRules[locale];
  if (pluralizer !== undefined) return pluralizer;
  return this.pluralizationRules["en"];
};

I18n.findAndTranslateValidNode = function(keys, translation) {
  for (var i = 0; i < keys.length; i++) {
    var key = keys[i];
    if (this.isValidNode(translation, key)) return translation[key];
  }
  return null;
};

I18n.pluralize = function(translation, scope, options) {
  if (typeof translation !== "object") return translation;

  options = this.prepareOptions(options);
  var count = options.count.toString();

  var pluralizer = this.pluralizer(options.locale || this.currentLocale());
  var key = pluralizer(Math.abs(count));
  var keys = typeof key === "object" && key instanceof Array ? key : [key];

  var message = this.findAndTranslateValidNode(keys, translation);

  if (message !== null || options.ignoreMissing) {
    return message;
  }

  return this.missingTranslation(scope, keys[0]);
};

I18n.missingTranslation = function(scope, key) {
  var message = "[" + this.currentLocale() + this.SEPARATOR + scope;
  if (key) {
    message += this.SEPARATOR + key;
  }
  return message + "]";
};

I18n.currentLocale = function() {
  return I18n.locale || I18n.defaultLocale;
};

I18n.enableVerboseLocalization = function() {
  var counter = 0;
  var keys = {};
  var t = I18n.t;

  I18n.noFallbacks = true;

  I18n.t = I18n.translate = function(scope, value) {
    var current = keys[scope];
    if (!current) {
      current = keys[scope] = ++counter;
      var message = "Translation #" + current + ": " + scope;
      if (value && Object.keys(value).length > 0) {
        message += ", parameters: " + JSON.stringify(value);
      }
      // eslint-disable-next-line no-console
      console.info(message);
    }
    return t.apply(I18n, [scope, value]) + " (#" + current + ")";
  };
};

I18n.enableVerboseLocalizationSession = function() {
  sessionStorage.setItem("verbose_localization", "true");
  I18n.enableVerboseLocalization();

  return "Verbose localization is enabled. Close the browser tab to turn it off. Reload the page to see the translation keys.";
};

// shortcuts
I18n.t = I18n.translate;