I'm running a WordPress blog in Greek, and the encoding I use is UTF-8, as it includes all Greek characters, and everything on the blog itself is displayed just fine. But when people share my posts on Facebook (or Google+), the characters are all messed up, and it looks something like this: http://i.imgur.com/RAJX8.png
Strangely, it only happens when I share an individual post, it doesn't happen when I share the blog's homepage: http://i.imgur.com/YFB2r.png
I've only found this other guy who had the very same issue, but his solution was for Drupal, so I don't really know WHAT to change on my WordPress code (and I can't say I'm the best coder around).
Could you fine gentlemen please help me resolve this?
Thank you very much.