At this time it does not appear to be possible to replace the fancy quotes with straight quotes using the markdown typographer quotation marks site setting. The original intention for that setting was to support languages such as German and French that would have four different quote characters.
With the enable markdown typographer site setting checked, the double quotes will be rendered as straight only when there is a space directly after the first double quote, or a space directly before the last double quote.
Straight quotes:
- " "
- " foo"
- "bar "
- " foo bar"
- "foo bar "
Fancy quotes:
- “”
- “foo”
- “foo bar”
Single quotes (aka an apostrophe) will always be rendered fancy.
Is there a particular reason you are looking to replace the fancy quotes? For the purposes of sharing code, we suggest using code blocks to bypass the fancy formatting:
Using the following syntax:
```
'single quote'
"double quote"
```
Will produce:
'single quote'
"double quote"