Error installing buildbot

(sandbox) MBP-de-MACBOOK:bb-master rachmann$ buildbot create-master master
Traceback (most recent call last):
  File "/Users/rachmann/tmp/bb-master/sandbox/lib/python3.7/site-packages/buildbot/util/__init__.py", line 360, in check_functional_environment
    locale.getdefaultlocale()
  File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/locale.py", line 568, in getdefaultlocale
    return _parse_localename(localename)
  File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/locale.py", line 495, in _parse_localename
    raise ValueError('unknown locale: %s' % localename)
ValueError: unknown locale: UTF-8

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/rachmann/tmp/bb-master/sandbox/bin/buildbot", line 10, in <module>
    sys.exit(run())
  File "/Users/rachmann/tmp/bb-master/sandbox/lib/python3.7/site-packages/buildbot/scripts/runner.py", line 753, in run
    check_functional_environment(buildbot.config)
  File "/Users/rachmann/tmp/bb-master/sandbox/lib/python3.7/site-packages/buildbot/util/__init__.py", line 365, in check_functional_environment
    " are either unset or set to a valid locale.", str(e)
  File "/Users/rachmann/tmp/bb-master/sandbox/lib/python3.7/site-packages/buildbot/config.py", line 81, in error
    raise ConfigErrors([error])
buildbot.config.ConfigErrors: Your environment has incorrect locale settings. This means python cannot handle strings safely.
 Please check 'LANG', 'LC_CTYPE', 'LC_ALL' and 'LANGUAGE' are either unset or set to a valid locale.
unknown locale: UTF-8
(sandbox) MBP-de-MACBOOK:bb-master rachmann$ buildbot create-master master
Traceback (most recent call last):
  File "/Users/rachmann/tmp/bb-master/sandbox/lib/python3.7/site-packages/