diff --git a/src/internationalization/PhutilTranslator.php b/src/internationalization/PhutilTranslator.php
index 5ed00bc..875c8c4 100644
--- a/src/internationalization/PhutilTranslator.php
+++ b/src/internationalization/PhutilTranslator.php
@@ -1,152 +1,169 @@
 <?php
 
 /**
  * @group internationalization
  */
 final class PhutilTranslator {
   static private $instance;
 
   private $language = 'en';
   private $translations = array();
 
   public static function getInstance() {
     if (self::$instance === null) {
       self::$instance = new PhutilTranslator();
     }
     return self::$instance;
   }
 
   public static function setInstance(PhutilTranslator $instance) {
     self::$instance = $instance;
   }
 
   public function setLanguage($language) {
     $this->language = $language;
     return $this;
   }
 
   /**
    * Add translations which will be later used by @{method:translate}.
    * The parameter is an array of strings (for simple translations) or arrays
    * (for translastions with variants). The number of items in the array is
    * language specific. It is `array($singular, $plural)` for English.
    *
    *   array(
    *     'color' => 'colour',
    *     '%d beer(s)' => array('%d beer', '%d beers'),
    *   );
    *
    * The arrays can be nested for strings with more variant parts:
    *
    *   array(
    *     '%d char(s) on %d row(s)' => array(
    *       array('%d char on %d row', '%d char on %d rows'),
    *       array('%d chars on %d row', '%d chars on %d rows'),
    *     ),
    *   );
    *
    * The translation should have the same placeholders as originals. Swapping
    * parameter order is possible:
    *
    *   array(
    *     '%s owns %s.' => '%2$s is owned by %1$s.',
    *   );
    *
    * @param array Identifier in key, translation in value.
    * @return PhutilTranslator Provides fluent interface.
    */
   public function addTranslations(array $translations) {
     $this->translations = array_merge($this->translations, $translations);
     return $this;
   }
 
   public function translate($text /* , ... */) {
     $translation = idx($this->translations, $text, $text);
     $args = func_get_args();
     while (is_array($translation)) {
       $translation = $this->chooseVariant($translation, next($args));
     }
     array_shift($args);
     return vsprintf($translation, $args);
   }
 
   private function chooseVariant(array $translations, $variant) {
     switch ($this->language) {
 
       case 'en':
         list($singular, $plural) = $translations;
         if ($variant == 1) {
           return $singular;
         }
         return $plural;
 
       case 'cs':
         if ($variant instanceof PhutilPerson) {
           list($male, $female) = $translations;
           if ($variant->getSex() == PhutilPerson::SEX_FEMALE) {
             return $female;
           }
           return $male;
         }
 
         list($singular, $paucal, $plural) = $translations;
         if ($variant == 1) {
           return $singular;
         }
         if ($variant >= 2 && $variant <= 4) {
           return $paucal;
         }
         return $plural;
 
       default:
         throw new Exception("Unknown language '{$this->language}'.");
     }
   }
 
   /**
    * Translate date formatted by `$date->format()`.
    *
    * @param string Format accepted by `DateTime::format()`.
    * @param DateTime
    * @return string Formatted and translated date.
    */
   public function translateDate($format, DateTime $date) {
     static $format_cache = array();
     if (!isset($format_cache[$format])) {
       $translatable = 'DlSFMaA';
       preg_match_all(
         '/['.$translatable.']|(\\\\.|[^'.$translatable.'])+/',
         $format,
         $format_cache[$format],
         PREG_SET_ORDER);
     }
 
     $parts = array();
     foreach ($format_cache[$format] as $match) {
       $part = $date->format($match[0]);
       if (!isset($match[1])) {
         $part = $this->translate($part);
       }
       $parts[] = $part;
     }
     return implode('', $parts);
   }
 
+  /**
+   * Format number with grouped thousands and optional decimal part. Requires
+   * translations of '.' (decimal point) and ',' (thousands separator). Both
+   * these translations must be 1 byte long.
+   *
+   * @param float
+   * @param int
+   * @return string
+   */
+  public function formatNumber($number, $decimals = 0) {
+    return number_format(
+      $number,
+      $decimals,
+      $this->translate('.'),
+      $this->translate(','));
+  }
+
   public function validateTranslation($original, $translation) {
     $pattern = '/<(\S[^>]*>?)?|&(\S[^;]*;?)?/i';
     $original_matches = null;
     $translation_matches = null;
 
     preg_match_all($pattern, $original, $original_matches);
     preg_match_all($pattern, $translation, $translation_matches);
 
     sort($original_matches[0]);
     sort($translation_matches[0]);
 
     if ($original_matches[0] !== $translation_matches[0]) {
       return false;
     }
     return true;
   }
 
 }
diff --git a/src/internationalization/__tests__/PhutilTranslatorTestCase.php b/src/internationalization/__tests__/PhutilTranslatorTestCase.php
index 1b13d2e..4c37f68 100644
--- a/src/internationalization/__tests__/PhutilTranslatorTestCase.php
+++ b/src/internationalization/__tests__/PhutilTranslatorTestCase.php
@@ -1,149 +1,165 @@
 <?php
 
 /**
  * @group testcase
  */
 final class PhutilTranslatorTestCase extends PhutilTestCase {
 
   public function testEnglish() {
     $translator = new PhutilTranslator();
     $translator->addTranslations(
       array(
         '%d line(s)' => array('%d line', '%d lines'),
         '%d char(s) on %d row(s)' => array(
           array('%d char on %d row', '%d char on %d rows'),
           array('%d chars on %d row', '%d chars on %d rows'),
         ),
       ));
 
     $this->assertEqual('line', $translator->translate('line'));
     $this->assertEqual('param', $translator->translate('%s', 'param'));
 
     $this->assertEqual('0 lines', $translator->translate('%d line(s)', 0));
     $this->assertEqual('1 line', $translator->translate('%d line(s)', 1));
     $this->assertEqual('2 lines', $translator->translate('%d line(s)', 2));
 
     $this->assertEqual(
       '1 char on 1 row',
       $translator->translate('%d char(s) on %d row(s)', 1, 1));
     $this->assertEqual(
       '5 chars on 2 rows',
       $translator->translate('%d char(s) on %d row(s)', 5, 2));
 
     $this->assertEqual('1 beer(s)', $translator->translate('%d beer(s)', 1));
   }
 
   public function testCzech() {
     $translator = new PhutilTranslator();
     $translator->setLanguage('cs');
     $translator->addTranslations(
       array(
         '%d beer(s)' => array('%d pivo', '%d piva', '%d piv'),
       ));
 
     $this->assertEqual('0 piv', $translator->translate('%d beer(s)', 0));
     $this->assertEqual('1 pivo', $translator->translate('%d beer(s)', 1));
     $this->assertEqual('2 piva', $translator->translate('%d beer(s)', 2));
     $this->assertEqual('5 piv', $translator->translate('%d beer(s)', 5));
 
     $this->assertEqual('1 line(s)', $translator->translate('%d line(s)', 1));
   }
 
   public function testPerson() {
     $translator = new PhutilTranslator();
     $translator->setLanguage('cs');
     $translator->addTranslations(
       array(
         '%s wrote.' => array('%s napsal.', '%s napsala.'),
       ));
 
     $person = new PhutilPersonTest();
     $this->assertEqual(
       'Test () napsal.',
       $translator->translate('%s wrote.', $person));
 
     $person->setSex(PhutilPerson::SEX_MALE);
     $this->assertEqual(
       'Test (m) napsal.',
       $translator->translate('%s wrote.', $person));
 
     $person->setSex(PhutilPerson::SEX_FEMALE);
     $this->assertEqual(
       'Test (f) napsala.',
       $translator->translate('%s wrote.', $person));
   }
 
   public function testTranslateDate() {
     $date = new DateTime('2012-06-21');
 
     $translator = new PhutilTranslator();
     $this->assertEqual('June', $translator->translateDate('F', $date));
     $this->assertEqual('June 21', $translator->translateDate('F d', $date));
     $this->assertEqual('F', $translator->translateDate('\F', $date));
 
     $translator->addTranslations(
       array(
         'June' => 'correct',
         '21' => 'wrong',
         'F' => 'wrong'
       ));
     $this->assertEqual('correct', $translator->translateDate('F', $date));
     $this->assertEqual('correct 21', $translator->translateDate('F d', $date));
     $this->assertEqual('F', $translator->translateDate('\F', $date));
   }
 
   public function testSetInstance() {
     PhutilTranslator::setInstance(new PhutilTranslator());
     $original = PhutilTranslator::getInstance();
     $this->assertEqual('color', pht('color'));
 
     $british = new PhutilTranslator();
     $british->addTranslations(
       array(
         'color' => 'colour',
       ));
     PhutilTranslator::setInstance($british);
     $this->assertEqual('colour', pht('color'));
 
     PhutilTranslator::setInstance($original);
     $this->assertEqual('color', pht('color'));
   }
 
+  public function testFormatNumber() {
+    $translator = new PhutilTranslator();
+    $this->assertEqual('1,234', $translator->formatNumber(1234));
+    $this->assertEqual('1,234.5', $translator->formatNumber(1234.5, 1));
+    $this->assertEqual('1,234.5678', $translator->formatNumber(1234.5678, 4));
+
+    $translator->addTranslations(
+      array(
+        ',' => ' ',
+        '.' => ','
+      ));
+    $this->assertEqual('1 234', $translator->formatNumber(1234));
+    $this->assertEqual('1 234,5', $translator->formatNumber(1234.5, 1));
+    $this->assertEqual('1 234,5678', $translator->formatNumber(1234.5678, 4));
+  }
+
   public function testValidateTranslation() {
     $tests = array(
       'a < 2' => array(
         'a < 2' => true,
         'b < 3' => true,
         '2 > a' => false,
         'a<2' => false,
       ),
       'We <em>win</em>' => array(
         'We <em>win</em>' => true,
         'We </em>win<em>' => true, // false positive
         'We win' => false,
         'We <em onmouseover="">win</em>' => false,
       ),
       'We <em title="%s">win</em> &amp; triumph' => array(
         'We <em title="%s">triumph</em> &amp; win' => true,
         'We <em title="%s">win</em> and triumph' => false,
       ),
       'beer' => array(
         'pivo' => true,
         'b<>r' => false,
         'b&&r' => false,
       ),
     );
 
     $translator = new PhutilTranslator();
     foreach ($tests as $original => $translations) {
       foreach ($translations as $translation => $expect) {
         $valid = ($expect ? "valid" : "invalid");
         $this->assertEqual(
           $expect,
           $translator->validateTranslation($original, $translation),
           "'{$original}' should be {$valid} with '{$translation}'.");
       }
     }
   }
 
 }