Problem: UnicodeDecodeError: 'ascii' codec can't decode byte 0xc0 in position 26: ordinal not in range(128)
S3cmd:   0.9.9.91

The bug appears if User Profile directory on Windows contains non-english symbols (for ex. if username contains Russian characters).

This seems to fix it:
File: s3cmd 
Line: #1472
config_file = os.path.join(os.getenv("USERPROFILE").decode('mbcs'), "Application Data", "s3cmd.ini")
Added ".decode('mbcs')"