diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -545,10 +545,12 @@
     'phutil_get_library_root' => 'moduleutils/moduleutils.php',
     'phutil_get_library_root_for_path' => 'moduleutils/moduleutils.php',
     'phutil_get_signal_name' => 'future/exec/execx.php',
+    'phutil_get_system_locale' => 'utils/utf8.php',
     'phutil_hashes_are_identical' => 'utils/utils.php',
     'phutil_implode_html' => 'markup/render.php',
     'phutil_ini_decode' => 'utils/utils.php',
     'phutil_is_hiphop_runtime' => 'utils/utils.php',
+    'phutil_is_system_locale_available' => 'utils/utf8.php',
     'phutil_is_utf8' => 'utils/utf8.php',
     'phutil_is_utf8_slowly' => 'utils/utf8.php',
     'phutil_is_utf8_with_only_bmp_characters' => 'utils/utf8.php',
@@ -563,6 +565,7 @@
     'phutil_register_library' => 'moduleutils/core.php',
     'phutil_register_library_map' => 'moduleutils/core.php',
     'phutil_safe_html' => 'markup/render.php',
+    'phutil_set_system_locale' => 'utils/utf8.php',
     'phutil_split_lines' => 'utils/utils.php',
     'phutil_tag' => 'markup/render.php',
     'phutil_tag_div' => 'markup/render.php',
diff --git a/src/utils/__tests__/PhutilUTF8TestCase.php b/src/utils/__tests__/PhutilUTF8TestCase.php
--- a/src/utils/__tests__/PhutilUTF8TestCase.php
+++ b/src/utils/__tests__/PhutilUTF8TestCase.php
@@ -739,4 +739,70 @@
     }
   }
 
+  public function testSystemLocaleManagement() {
+    $original_locale = phutil_get_system_locale();
+    $this->assertTrue(
+      (strlen($original_locale) > 0),
+      pht('System has some identifiable locale.'));
+
+    $this->assertFalse(
+      phutil_is_system_locale_available('duck.quack'),
+      pht('Imaginary locale should be unavailable.'));
+
+    $this->assertEqual(
+      $original_locale,
+      phutil_get_system_locale(),
+      pht('Testing locale availability should not change the locale.'));
+
+    $this->assertTrue(
+      phutil_is_system_locale_available($original_locale),
+      pht('The current locale should be available.'));
+
+    $caught = null;
+    try {
+      phutil_set_system_locale('duck.quack');
+    } catch (Exception $ex) {
+      $caught = $ex;
+    }
+
+    $this->assertTrue(
+      ($caught instanceof Exception),
+      pht('Setting an imaginary locale should raise an exception.'));
+
+    // We need two locales for the next part because one of them might be the
+    // current locale, and we want to make sure we can actually change the
+    // locale value.
+
+    // If the current locale was "zz_ZZ", and then we do this:
+    //
+    //   set_locale("zz_ZZ");
+    //   assert("zz_ZZ" == get_locale());
+    //
+    // ...the test could pass even if "set_locale(...)" does nothing.
+
+    $has_us = phutil_is_system_locale_available('en_US.UTF-8');
+    $has_gb = phutil_is_system_locale_available('en_GB.UTF-8');
+    if (!$has_us || !$has_gb) {
+      $this->assertSkipped(
+        pht(
+          'System does not have en_US + en_GB to do locale adjustment '.
+          'tests.'));
+    }
+
+    phutil_set_system_locale('en_US.UTF-8');
+    $this->assertEqual(
+      'en_US.UTF-8',
+      phutil_get_system_locale(),
+      pht('Set locale to en_US.'));
+
+    phutil_set_system_locale('en_GB.UTF-8');
+    $this->assertEqual(
+      'en_GB.UTF-8',
+      phutil_get_system_locale(),
+      pht('Set locale to en_GB.'));
+
+    // Put things back the way they were.
+    phutil_set_system_locale($original_locale);
+  }
+
 }
diff --git a/src/utils/utf8.php b/src/utils/utf8.php
--- a/src/utils/utf8.php
+++ b/src/utils/utf8.php
@@ -897,3 +897,54 @@
 
   return $parts;
 }
+
+
+/**
+ * Return the current system locale setting (LC_ALL).
+ *
+ * @return string Current system locale setting.
+ */
+function phutil_get_system_locale() {
+  $locale = setlocale(LC_ALL, 0);
+
+  if ($locale === false) {
+    throw new Exception(
+      pht(
+        'Unable to determine current system locale (call to '.
+        '"setlocale(LC_ALL, 0)" failed).'));
+  }
+
+  return $locale;
+}
+
+
+/**
+ * Test if a system locale (LC_ALL) is available on the system.
+ *
+ * @param string Locale name like "en_US.UTF-8".
+ * @return bool True if the locale is available.
+ */
+function phutil_is_system_locale_available($locale) {
+  $old_locale = phutil_get_system_locale();
+  $is_available = @setlocale(LC_ALL, $locale);
+  setlocale(LC_ALL, $old_locale);
+
+  return ($is_available !== false);
+}
+
+
+/**
+ * Set the system locale (LC_ALL) to a particular value.
+ *
+ * @param string New locale setting.
+ * @return void
+ */
+function phutil_set_system_locale($locale) {
+  $ok = @setlocale(LC_ALL, $locale);
+  if (!$ok) {
+    throw new Exception(
+      pht(
+        'Failed to set system locale (to "%s").',
+        $locale));
+  }
+}