UnicodeEncodeError when path contains non-ascii characters

[cbrnr]

Whenever the path (which includes the file name) contains a non-ascii character (e.g. the German ü), I get a warning message in Atom, which is caused by a UnicodeEncodeError in flake8:

linter-flake8:: Flake8 returned an error Traceback (most recent call last):
  File "/usr/local/bin/flake8", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.6/site-packages/flake8/main/cli.py", line 16, in main
    app.run(argv)
  File "/usr/local/lib/python3.6/site-packages/flake8/main/application.py", line 396, in run
    self._run(argv)
  File "/usr/local/lib/python3.6/site-packages/flake8/main/application.py", line 385, in _run
    self.report()
  File "/usr/local/lib/python3.6/site-packages/flake8/main/application.py", line 376, in report
    self.report_errors()
  File "/usr/local/lib/python3.6/site-packages/flake8/main/application.py", line 340, in report_errors
    results = self.file_checker_manager.report()
  File "/usr/local/lib/python3.6/site-packages/flake8/checker.py", line 267, in report
    results_reported += self._handle_results(filename, results)
  File "/usr/local/lib/python3.6/site-packages/flake8/checker.py", line 166, in _handle_results
    physical_line=physical_line,
  File "/usr/local/lib/python3.6/site-packages/flake8/style_guide.py", line 392, in handle_error
    self.formatter.handle(error)
  File "/usr/local/lib/python3.6/site-packages/flake8/formatting/base.py", line 88, in handle
    self.write(line, source)
  File "/usr/local/lib/python3.6/site-packages/flake8/formatting/base.py", line 191, in write
    self._write(line)
  File "/usr/local/lib/python3.6/site-packages/flake8/formatting/base.py", line 175, in _write
    print(output)
UnicodeEncodeError: 'ascii' codec can't encode character '\u0308' in position 24: ordinal not in range(128)

This error disappears if I remove the non-ascii characters from the file name/path.

I've already created an issue at https://gitlab.com/pycqa/flake8/issues/420, but I feel this is an issue of linter-flake8 because this works if I use flake8 from the command line. @sigmavirus24 commented that it might have to do with non-matching locales. Please let me know if you need further information.