I mapped the most common strange chars so this is pretty much complete answer based on the Oliver W. answer.
This function is by no means ideal,but it is the best place to start with.
There are more chars definitions:
http://utf8-chartable.de/unicode-utf8-table.pl?start=8192&number=128&utf8=string
http://www.utf8-chartable.de/unicode-utf8-table.pl?start=128&number=128&names=-&utf8=string-literal
...
def unicodetoascii(text):
uni2ascii = {
ord('\xe2\x80\x99'.decode('utf-8')): ord("'"),
ord('\xe2\x80\x9c'.decode('utf-8')): ord('"'),
ord('\xe2\x80\x9d'.decode('utf-8')): ord('"'),
ord('\xe2\x80\x9e'.decode('utf-8')): ord('"'),
ord('\xe2\x80\x9f'.decode('utf-8')): ord('"'),
ord('\xc3\xa9'.decode('utf-8')): ord('e'),
ord('\xe2\x80\x9c'.decode('utf-8')): ord('"'),
ord('\xe2\x80\x93'.decode('utf-8')): ord('-'),
ord('\xe2\x80\x92'.decode('utf-8')): ord('-'),
ord('\xe2\x80\x94'.decode('utf-8')): ord('-'),
ord('\xe2\x80\x94'.decode('utf-8')): ord('-'),
ord('\xe2\x80\x98'.decode('utf-8')): ord("'"),
ord('\xe2\x80\x9b'.decode('utf-8')): ord("'"),
ord('\xe2\x80\x90'.decode('utf-8')): ord('-'),
ord('\xe2\x80\x91'.decode('utf-8')): ord('-'),
ord('\xe2\x80\xb2'.decode('utf-8')): ord("'"),
ord('\xe2\x80\xb3'.decode('utf-8')): ord("'"),
ord('\xe2\x80\xb4'.decode('utf-8')): ord("'"),
ord('\xe2\x80\xb5'.decode('utf-8')): ord("'"),
ord('\xe2\x80\xb6'.decode('utf-8')): ord("'"),
ord('\xe2\x80\xb7'.decode('utf-8')): ord("'"),
ord('\xe2\x81\xba'.decode('utf-8')): ord("+"),
ord('\xe2\x81\xbb'.decode('utf-8')): ord("-"),
ord('\xe2\x81\xbc'.decode('utf-8')): ord("="),
ord('\xe2\x81\xbd'.decode('utf-8')): ord("("),
ord('\xe2\x81\xbe'.decode('utf-8')): ord(")"),
}
return text.decode('utf-8').translate(uni2ascii).encode('ascii')
print unicodetoascii("weren\xe2\x80\x99t")