Начиная с drupal 6 появилась возможность пользоваться переводами в JavaScript

Используются аналоги:
Drupal.t(строка, {массив параметров}) - синоним t()
Drupal.formatPlural(количество, единственная форма, множественная форма, массив параметров) format_plural()

/**
 * Translate strings to the page language or a given language.
 *
 * See the documentation of the server-side t() function for further details.
 *
 * @param str
 *   A string containing the English string to translate.
 * @param args
 *   An object of replacements pairs to make after translation. Incidences
 *   of any key in this array are replaced with the corresponding value.
 *   Based on the first character of the key, the value is escaped and/or themed:
 *    - !variable: inserted as is
 *    - @variable: escape plain text to HTML (Drupal.checkPlain)
 *    - %variable: escape text and theme as a placeholder for user-submitted
 *      content (checkPlain + Drupal.theme('placeholder'))
 * @return
 *   The translated string.
 */
Drupal.t = function(str, args) {
  // Fetch the localized version of the string.
  if (Drupal.locale.strings && Drupal.locale.strings[str]) {
    str = Drupal.locale.strings[str];
  }

  if (args) {
    // Transform arguments before inserting them
    for (var key in args) {
      switch (key.charAt(0)) {
        // Escaped only
        case '@':
          args[key] = Drupal.checkPlain(args[key]);
        break;
        // Pass-through
        case '!':
          break;
        // Escaped and placeholder
        case '%':
        default:
          args[key] = Drupal.theme('placeholder', args[key]);
          break;
      }
      str = str.replace(key, args[key]);
    }
  }
  return str;
};

/**
 * Format a string containing a count of items.
 *
 * This function ensures that the string is pluralized correctly. Since Drupal.t() is
 * called by this function, make sure not to pass already-localized strings to it.
 *
 * See the documentation of the server-side format_plural() function for further details.
 *
 * @param count
 *   The item count to display.
 * @param singular
 *   The string for the singular case. Please make sure it is clear this is
 *   singular, to ease translation (e.g. use "1 new comment" instead of "1 new").
 *   Do not use @count in the singular string.
 * @param plural
 *   The string for the plural case. Please make sure it is clear this is plural,
 *   to ease translation. Use @count in place of the item count, as in "@count
 *   new comments".
 * @param args
 *   An object of replacements pairs to make after translation. Incidences
 *   of any key in this array are replaced with the corresponding value.
 *   Based on the first character of the key, the value is escaped and/or themed:
 *    - !variable: inserted as is
 *    - @variable: escape plain text to HTML (Drupal.checkPlain)
 *    - %variable: escape text and theme as a placeholder for user-submitted
 *      content (checkPlain + Drupal.theme('placeholder'))
 *   Note that you do not need to include @count in this array.
 *   This replacement is done automatically for the plural case.
 * @return
 *   A translated string.
 */
Drupal.formatPlural = function(count, singular, plural, args) {
  var args = args || {};
  args['@count'] = count;
  // Determine the index of the plural form.
  var index = Drupal.locale.pluralFormula ? Drupal.locale.pluralFormula(args['@count']) : ((args['@count'] == 1) ? 0 : 1);

  if (index == 0) {
    return Drupal.t(singular, args);
  }
  else if (index == 1) {
    return Drupal.t(plural, args);
  }
  else {
    args['@count['+ index +']'] = args['@count'];
    delete args['@count'];
    return Drupal.t(plural.replace('@count', '@count['+ index +']'), args);
  }
};

Официальная информация: изменения в drupal 6 и JavaScript localization issue

Подробная статья Translations in Drupal 6