Hard crash in logger due to codec issues

[sanderland]

Software Versions

• Python: 3.7
• OS: Windows 10
• Kivy: 2.0.0rc2
• Kivy installation method: pypi

Describe the bug
When setting logging level to trace, _write_message can crash with a UnicodeError

Expected behavior
Never hard crash while logging.

Probably there is some issue with picking up the codec, but logging binary strings with a catch Exception: something went wrong would be better than the current behaviour.

To Reproduce
Have a Korean version of windows 10 (which has the default cp949 codec) and a function call which returns a utf-8 string with special characters in a kv file.

Code and Logs and screenshots

 kivy.lang.builder.BuilderException: Parser: File "C:\Users\sande\Desktop\katrain\katrain\popups.kv", line 56:
 ...
      54:<I18NPopup>:
      55:    background_color: [*[c*255/66 for c in BACKGROUND_COLOR[:3]], 1]
 >>   56:    title: i18n._(self.title_key)
      57:    title_size: DESC_FONT_SIZE
      58:    title_font: self.font_name
 ...

 UnicodeEncodeError: 'cp949' codec can't encode character '\xe8' in position 29: illegal multibyte sequence
   File "C:\Users\sande\Anaconda3\lib\site-packages\kivy\lang\builder.py", line 699, in _apply_rule
     setattr(widget_set, key, value)
   File "kivy\weakproxy.pyx", line 35, in kivy.weakproxy.WeakProxy.__setattr__
   File "kivy\properties.pyx", line 497, in kivy.properties.Property.__set__
   File "kivy\properties.pyx", line 544, in kivy.properties.Property.set
   File "kivy\properties.pyx", line 599, in kivy.properties.Property.dispatch
   File "kivy\_event.pyx", line 1248, in kivy._event.EventObservers.dispatch
   File "kivy\_event.pyx", line 1130, in kivy._event.EventObservers._dispatch
   File "C:\Users\sande\Anaconda3\lib\site-packages\kivy\lang\builder.py", line 68, in call_fn
     trace('Lang: call_fn => value=%r' % (e_value, ))
   File "C:\Users\sande\Anaconda3\lib\logging\__init__.py", line 1449, in log
     self._log(level, msg, args, **kwargs)
   File "C:\Users\sande\Anaconda3\lib\logging\__init__.py", line 1519, in _log
     self.handle(record)
   File "C:\Users\sande\Anaconda3\lib\logging\__init__.py", line 1529, in handle
     self.callHandlers(record)
   File "C:\Users\sande\Anaconda3\lib\logging\__init__.py", line 1591, in callHandlers
     hdlr.handle(record)
   File "C:\Users\sande\Anaconda3\lib\logging\__init__.py", line 905, in handle
     self.emit(record)
   File "C:\Users\sande\Anaconda3\lib\site-packages\kivy\logger.py", line 263, in emit
     self._write_message(message)
   File "C:\Users\sande\Anaconda3\lib\site-packages\kivy\logger.py", line 234, in _write_message
     stream.write(fs % msg)

[matham]

#6910