即使手动安装了所有依赖项，也无法使用pip安装Seaborn

$ pip install seaborn

Collecting seaborn
  Using cached seaborn-0.7.0.tar.gz
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):
      File "<string>", line 1, in <module>
      File "/private/var/folders/hf/hf0xmv_d6mb0n4qp6xqkq0sh0000gn/T/pip-build-UpeZ8b/seaborn/setup.py", line 66, in <module>
        install_requires = check_dependencies()
      File "/private/var/folders/hf/hf0xmv_d6mb0n4qp6xqkq0sh0000gn/T/pip-build-UpeZ8b/seaborn/setup.py", line 54, in check_dependencies
        import matplotlib
      File "/usr/local/lib/python2.7/site-packages/matplotlib/__init__.py", line 1131, in <module>
        rcParams = rc_params()
      File "/usr/local/lib/python2.7/site-packages/matplotlib/__init__.py", line 975, in rc_params
        return rc_params_from_file(fname, fail_on_error)
      File "/usr/local/lib/python2.7/site-packages/matplotlib/__init__.py", line 1100, in rc_params_from_file
        config_from_file = _rc_params_in_file(fname, fail_on_error)
      File "/usr/local/lib/python2.7/site-packages/matplotlib/__init__.py", line 1018, in _rc_params_in_file
        with _open_file_or_url(fname) as fd:
      File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/contextlib.py", line 17, in __enter__
        return self.gen.next()
      File "/usr/local/lib/python2.7/site-packages/matplotlib/__init__.py", line 1000, in _open_file_or_url
        encoding = locale.getdefaultlocale()[1]
      File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/locale.py", line 543, in getdefaultlocale
        return _parse_localename(localename)
      File "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/locale.py", line 475, in _parse_localename
        raise ValueError, 'unknown locale: %s' % localename
    ValueError: unknown locale: UTF-8

    ----------------------------------------
Command "python setup.py egg_info" failed with error code 1 in /private/var/folders/hf/hf0xmv_d6mb0n4qp6xqkq0sh0000gn/T/pip-build-UpeZ8b/seaborn

我已经为Seaborn安装了所有必要的依赖项（matplotlib，scipy，numpy，pandas，statsmodels；没有任何用处。我在做什么错了？