The problem is that in many blogs and other websites they do the opposite: you enter data with the keyboard default quotes (vertical) and when you submit they convert them to curly ones ( they can do for example with http://pastebin.com/CEK0NN43 ). If the submited data is a computer code you have normally to put the quotes as straight again so the code works.

In client side they do the opposite like shown in http://stackoverflow.com/questions/2202811/converting-straight-quotes-to-curly-quotes

Just remove the blank space after the first character (less-than, similar to bracket.

I get “ before “ or “ (left double quotation mark) and ” after ” or ” (right double quotation mark).

For me works well this function:

Adapted from http://www.toao.net/48-replacing-smart-quotes-and-em-dashes-in-mysql

$allEntities = get_html_translation_table(HTML_ENTITIES, ENT_NOQUOTES);
$specialEntities = get_html_translation_table(HTML_SPECIALCHARS, ENT_NOQUOTES);
$noTags = array_diff($allEntities, $specialEntities);

And, that will leave tags alone, assuming that's what you want.
$valid = strtr($invalid, $noTags);

Don