I have the same problem. My ebooks are in PDB format with english LEFT DOUBLE QUOTATION MARK (Unicode201C - ALT 0147) at the beginning of direct speach and RIGHT DOUBLE QUOTATION MARK (Unicode201D - ALT 0148) at the ending. I need to change it to czech file format with quotation mark Uicode201E - ALT 0132 at the beginning and quotation mark Unicode201C - ALT 0147 at the ending.
When I search the left english quotation mark in regex builder (I enter ALT 0147 and press TEST) it finds all occurrences and marks them with yellow color. But when I do the same in Search&Replace (search ALT 0147 and replace with WHATEVER CHARACTER e.g. Q ) no changes are made
Search of ALT 0148 is the same result.
I must open my ebooks in other text editor, replace quotation marks as I wish and then open it in calibre and convert to my favorit MOBI format.
Thanks for any help