pandas 0.23.4 fails unit tests
#### Problem description

Cannot seem to complete unit tests on a source install of pandas 0.23.4. I'm sure I'm doing something dumb, but cannot see what. Any ideas, please?

#### Code Sample, a copy-pastable example if possible

```python
$ python
Python 3.6.0 (default, Feb 22 2017, 16:36:12) 
[GCC 6.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas
>>> pandas.test()
running: pytest --skip-slow --skip-network /somewhere/py_new/build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas
============================= test session starts ==============================
platform linux -- Python 3.6.0, pytest-3.9.3, py-1.7.0, pluggy-0.8.0
rootdir: /somewhere/py_new, inifile:
plugins: cov-2.6.0
collected 26659 items / 3 errors / 2 skipped

==================================== ERRORS ====================================
 ERROR collecting build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/indexes/datetimes/test_misc.py 
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/indexes/datetimes/test_misc.py:90: in <module>
    class TestDatetime64(object):
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/indexes/datetimes/test_misc.py:246: in TestDatetime64
    None] if tm.get_locales() is None else [None] + tm.get_locales())
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/util/testing.py:456: in get_locales
    x, encoding=pd.options.display.encoding))
E   UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe5 in position 4: invalid continuation byte
 ERROR collecting build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/scalar/timestamp/test_timestamp.py 
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/scalar/timestamp/test_timestamp.py:28: in <module>
    class TestTimestampProperties(object):
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/scalar/timestamp/test_timestamp.py:104: in TestTimestampProperties
    None] if tm.get_locales() is None else [None] + tm.get_locales())
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/util/testing.py:456: in get_locales
    x, encoding=pd.options.display.encoding))
E   UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe5 in position 4: invalid continuation byte
 ERROR collecting build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/series/test_datetime_values.py 
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/series/test_datetime_values.py:25: in <module>
    class TestSeriesDatetimeValues(TestData):
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/series/test_datetime_values.py:280: in TestSeriesDatetimeValues
    None] if tm.get_locales() is None else [None] + tm.get_locales())
build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/util/testing.py:456: in get_locales
    x, encoding=pd.options.display.encoding))
E   UnicodeDecodeError: 'utf-8' codec can't decode byte 0xe5 in position 4: invalid continuation byte
=============================== warnings summary ===============================
build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "df_letters" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "df_letters" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "epoch_1960" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "epoch_1960" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "epoch_1960" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)
  /somewhere/py_new/build/lib/python3.6/site-packages/pytest-3.9.3-py3.6.egg/_pytest/assertion/rewrite.py:294: RemovedInPytest4Warning: Fixture "epoch_1960" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    six.exec_(co, mod.__dict__)

build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/series/test_analytics.py:1882
  /somewhere/py_new/build/lib/python3.6/site-packages/pandas-0.23.4-py3.6-linux-x86_64.egg/pandas/tests/series/test_analytics.py:1882: RemovedInPytest4Warning: Fixture "s_main_dtypes" called directly. Fixtures are not meant to be called directly, are created automatically when test functions request them as parameters. See https://docs.pytest.org/en/latest/fixture.html for more information.
    class TestNLargestNSmallest(object):

-- Docs: https://docs.pytest.org/en/latest/warnings.html
!!!!!!!!!!!!!!!!!!! Interrupted: 3 errors during collection !!!!!!!!!!!!!!!!!!!!
=============== 2 skipped, 7 warnings, 3 error in 49.24 seconds ================
```

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.0.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0-693.11.6.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_GB.utf8
LOCALE: en_GB.UTF-8

pandas: 0.23.4
pytest: 3.9.3
pip: 18.1
setuptools: 40.5.0
Cython: 0.29
numpy: 1.15.3
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 7.1.1
sphinx: 1.8.1
patsy: None
dateutil: 2.7.5
pytz: 2018.7
blosc: None
bottleneck: 1.2.1
tables: 3.4.4
numexpr: 2.6.8
feather: None
matplotlib: 3.0.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
</details>
