I have a lot of txt files containing product description written in English or other languages. I'm only interested in the txt files containing English. I do not know all the languages the txt may be written in. Those non-English description may also contain English characters such as a url. Is there any algorithm to calculate the ratio of English characters (excluding punctuation) so that if there are more than 50% non-English characters in the txt file, the file will be discarded.