add support for CLIENT_LANGUAGE setting
diff --git a/tools/run_tests/run_performance_tests.py b/tools/run_tests/run_performance_tests.py
index a7728e7..181d62b 100755
--- a/tools/run_tests/run_performance_tests.py
+++ b/tools/run_tests/run_performance_tests.py
@@ -304,7 +304,11 @@
           # 'SERVER_LANGUAGE' is an indicator for this script to pick
           # a server in different language.
           custom_server_lang = scenario_json.get('SERVER_LANGUAGE', None)
+          custom_client_lang = scenario_json.get('CLIENT_LANGUAGE', None)
           scenario_json = scenario_config.remove_nonproto_fields(scenario_json)
+          if custom_server_lang and custom_client_lang:
+            raise Exception('Cannot set both custom CLIENT_LANGUAGE and SERVER_LANGUAGE'
+                            'in the same scenario')
           if custom_server_lang:
             if not workers_by_lang.get(custom_server_lang, []):
               print 'Warning: Skipping scenario %s as' % scenario_json['name']
@@ -314,6 +318,16 @@
             for idx in range(0, scenario_json['num_servers']):
               # replace first X workers by workers of a different language
               workers[idx] = workers_by_lang[custom_server_lang][idx]
+          if custom_client_lang:
+            if not workers_by_lang.get(custom_client_lang, []):
+              print 'Warning: Skipping scenario %s as' % scenario_json['name']
+              print('CLIENT_LANGUAGE is set to %s yet the language has '
+                    'not been selected with -l' % custom_client_lang)
+              continue
+            for idx in range(scenario_json['num_servers'], len(workers)):
+              # replace all client workers by workers of a different language,
+              # leave num_server workers as they are server workers.
+              workers[idx] = workers_by_lang[custom_client_lang][idx]
           scenario = create_scenario_jobspec(scenario_json,
                                              workers,
                                              remote_host=remote_host,
@@ -360,8 +374,8 @@
                   help='Bigquery "dataset.table" to upload results to.')
 argp.add_argument('--category',
                   choices=['smoketest','all'],
-                  default='smoketest',
-                  help='Select a category of tests to run. Smoketest runs by default.')
+                  default='all',
+                  help='Select a category of tests to run.')
 argp.add_argument('--netperf',
                   default=False,
                   action='store_const',