Quite aside from the ambiguity of problems of apostrophes, the difficulty of writing curved single quotes has been mentioned. Here's how a totally different, unrelated wiki program could work:
//italics// **bold** ' - straight apostrophe 'single quotes'' '''backwards single quotes'''
In other words, ' is rendered like the current apostrophe, and '' is a curved apostrophe that leans either way depending on what text is immediately adjacent. And for those cases where you want the quotes to lean the *other* way, ''' just does the opposite of whatever '' does.
There has to be a better way, surely. Anything using the same character for different things is going to run into trouble...
I guess an alternative could use the "backquote":
Until you actually want to use a backquote. Doesn't happen very often in English, but does it get used in other languages?