l.js

/**
  The `{{l}}` helper renders a localized string using `I18n.l`.

  ```handlebars
  {{l "percentage" value=123.45}}
  ```

  ```html
  123.450%
  ```

  To pass additional configurations, simply provide them as
  attributes to the helper.

  ```handlebars
  {{l "number" value=1000 delimiter='.' separator=','}}
  ```

  ```html
  1.000,00
  ```

  If the localization string is generated via a bound value,
  you may generate your string by specifying the bound values
  using a quasi-literal:

  ```handlebars
  {{l "date.formats.`size`" value="2009-09-18"}}
  ```

  If `size` is `"short"`, then the resulting HTML would be:

  ```html
  "Sep 18, 2009"
  ```

  If `size` is `"long"`, then the resulting HTML would be:

  ```html
  "September 18, 2009"
  ```

  @method l
  @for Em.Handlebars.helpers
  @param string  {String} The string to localize
  @param formats {Object} An object to format the string with.
  @return {String} HTML string
 */
Ember.Handlebars.registerTextHelper('l', function (scope, context) {
  var value = context.value,
      SafeString = Ember.Handlebars.SafeString;

  switch (scope) {
  case "currency":
    return new SafeString(I18n.toCurrency(value, context));
  case "number":
    return new SafeString(I18n.toNumber(value, context));
  case "percentage":
    return new SafeString(I18n.toPercentage(value, context));
  default:
    if (scope.match(/^(date|time)/)) {
      // Fix for our dates which are in UTC
      if (scope.match(/^date/)) {
        value = value.toUTCString().replace(/GMT/, '');
      }
      return new SafeString(I18n.toTime(scope, value));
    } else {
      return value.toString();
    }
  }
}, /`(.*?)`/g);

What library to do you use for I18n.toCurrency and I18n.toPercent ?