diff --git a/simulator_control/simulator_util.py b/simulator_control/simulator_util.py
index 0f186fe..20b9844 100644
--- a/simulator_control/simulator_util.py
+++ b/simulator_control/simulator_util.py
@@ -113,13 +113,20 @@ def device_plist_object(self):
       self._device_plist_object = plist_util.Plist(device_plist_path)
     return self._device_plist_object
 
-  def Boot(self):
+  def Boot(self, simulator_language=None):
     """Boots the simulator as asynchronously.
 
+    Args:
+      simulator_language: string, the language of the simulator at startup time, e.g. 'ja'.
     Returns:
       A subprocess.Popen object of the boot process.
     """
     RunSimctlCommand(['xcrun', 'simctl', 'boot', self.simulator_id])
+    if simulator_language:
+      RunSimctlCommand(['xcrun', 'simctl', 'spawn', self.simulator_id,
+          'defaults', 'write', 'Apple Global Domain', 'AppleLanguages',
+          '-array', simulator_language])
+      RespringAllSimulators()
     self.WaitUntilStateBooted()
     logging.info('The simulator %s is booted.', self.simulator_id)
 
@@ -305,7 +312,7 @@ def GetSimulatorState(self):
     return _SIMULATOR_STATES_MAPPING[state_num]
 
 
-def CreateNewSimulator(device_type=None, os_version=None, name_prefix=None):
+def CreateNewSimulator(device_type=None, os_version=None, name_prefix=None, language=None):
   """Creates a new simulator according to arguments.
 
   If neither device_type nor os_version is given, will use the latest iOS
@@ -663,6 +670,13 @@ def QuitSimulatorApp():
                    stderr=subprocess.STDOUT)
 
 
+def RespringAllSimulators():
+  """Restarts the SpringBoard.app in all booted simulator."""
+  subprocess.Popen(['killall', '-HUP', 'SpringBoard'],
+                   stdout=subprocess.PIPE,
+                   stderr=subprocess.STDOUT)
+
+
 def IsAppFailedToLaunchOnSim(sim_sys_log, app_bundle_id=''):
   """Checks if the app failed to launch on simulator.
 
diff --git a/test_runner/ios_test_runner.py b/test_runner/ios_test_runner.py
index c85800d..27307d6 100644
--- a/test_runner/ios_test_runner.py
+++ b/test_runner/ios_test_runner.py
@@ -191,7 +191,7 @@ def _RunSimulatorTest(args):
       hostless = args.app_under_test_path is None
       try:
         if not hostless:
-          simulator_obj.Boot()
+          simulator_obj.Boot(args.simulator_language)
         session.Prepare(
             app_under_test=args.app_under_test_path,
             test_bundle=args.test_bundle_path,
@@ -238,6 +238,10 @@ def _SimulatorTest(args):
            'The new simulator name will be the value of concatenating name '
            'prefix with simulator type and os version. '
            'E.g., New-iPhone 6 Plus-10.2.')
+  test_parser.add_argument(
+      '--simulator_language',
+      help='The system language of the simulator at creation time, e.g `ja`. '
+           'Note: Do not set this if you create multiple simulators simutaneously.')
   test_parser.set_defaults(func=_SimulatorTest)